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Sample records for superior fatigue behavior

  1. Thermal fatigue behavior of K465 superalloy

    Institute of Scientific and Technical Information of China (English)

    YANG Jinxia; ZHENG Qi; SUN Xiaofeng; GUAN Hengrong; HU Zhuangqi

    2006-01-01

    The thermal fatigue behavior of K465 superalloy was investigated at the peak temperature of 1050℃. By scanning electron microscopy (SEM) and optical microscopy, the main crack length was observed and measured. The initiation sites of the tested alloys are different in as-cast (named as K465) and solution heat treatment (named as SK465) conditions.In K465 alloy, most thermal fatigue cracks nucleate at (Nb,W,Ti)C carbides. In SK465 alloy, thermal fatigue cracks initiate in interdendritic regions, MC-type carbides and some interfaces. Thermal fatigue cracks propagate in transdendritic mode,and M6C-type carbides could retard thermal fatigue crack growth for SK465 superalloy.

  2. The monotonic and fatigue behavior of CFCCs

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J. [Univ. of Tennessee, Knoxville, TN (United States); Snead, L.L. [Oak Ridge National Laboratory, TN (United States)

    1996-04-01

    Flexure tests were performed to study the fabric orientation effects on the monotonic and fatigue behavior of two commercially available continuous fiber reinforced ceramic composites (CFCCs), namely (i) Nicalon fiber fabric reinforced alumina (Al{sub 2}O{sub 3}) matrix composite fabricated by a direct molten metal oxidation (DIMOX) process and, (ii) Nicalon fiber fabric reinforced silicon carbide (SiC) matrix composite fabricated by an isothermal chemical vapor infiltration (ICVI) process. The fabric orientation effects on the monotonic and fatigue behavior were strong in the Nicalon/Al{sub 2}O{sub 3} composite, while they were relatively weak in the Nicalon/SiC composite.

  3. Fatigue Behaviors of Self-Piercing Rivets Joining Similar and Dissimilar Sheet Metals

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2007-01-01

    This paper summarizes the fatigue test results of self-piercing rivet (SPR) joints between similar and dissimilar sheet metals. The influences of material grades, material thickness, piercing direction and the use of structural adhesive on the rivet samples’ fatigue behaviors were investigated. Fatigue test results indicate that SPR joints have superior fatigue strength than resistance spot weld (RSW) joints for the same material combinations. The application of structure adhesive also significantly enhances the fatigue strength of the joint samples; this is particularly true for the lap shear loading configuration. In addition, different piercing directions for SPR joints have a noticeable effect on the static and fatigue strength of the joints. The joint fatigue results presented in this paper can offer design engineers with the durability data for SPR joints with these material combinations. Moreover, it will provide manufacturing engineers with some insights on the effects of different manufacturing parameters on the strength and durability of these joints.

  4. Fatigue behavior and encrustation characteristics of nanocrystalline metals

    Science.gov (United States)

    Lai, Li-Chung

    structures were investigated using transmission electron microscope (TEM). Crack tip grain growth was observed at early state of crack propagation with low stress intensity factor (K ˜ 6 MPa m 1/2). As K increased, the size of grain growth zone increased exponentially in width and crack propagation behavior transmitted from interganular to transgranular. It appears that this transmission is associated with grain growth. The coalesced grains due to grain rotation/GB diffusion created larger paths for more extended dislocation movement. Dislocation activities become less forbidden and the dislocation-slip mechanism can be dominant leading to a more plastically transgranular fracture. In addition to fatigue study of ED NC Ni, encrustation on ED NC Ti was investigated. The use of materials for medical applications in the urinary tract is hampered by the formation of calcium-based crystalline deposits, generally referred to as encrustation, that act as precursors to urinary stones. Anecdotal evidence suggests that titanium can possess encrustation-resistant properties in vivo and may be useful in urologic applications. To test the utility of coating surfaces with nanostructured titanium, several forms of materials were submersed in artificial urine with saturating concentrations of calcium for a period of 14 days. The specimens were then analyzed using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) to determine the extent of encrustation on the surface of the various samples. Our observations indicate that nanostructured titanium offers superior resistance to encrustation when compared to polyurethane, polyvinyl chloride or conventional coarser grained titanium. Further studies investigating the use of nanostructured titanium in urologic applications are warranted.

  5. Corrosion Fatigue Crack Growth Behavior at Notched Hole in 7075-T6 Under Biaxial and Uniaxial Fatigue with Different Phases

    Science.gov (United States)

    2015-09-17

    CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH DIFFERENT PHASES... CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH DIFFERENT PHASES THESIS...UNLIMITED AFIT-ENY-MS-15-S-065 CORROSION FATIGUE CRACK GROWTH BEHAVIOR AT NOTCHED HOLE IN 7075-T6 UNDER BIAXIAL AND UNIAXIAL FATIGUE WITH

  6. Fatigue behavior of ADI: Some specific features

    Energy Technology Data Exchange (ETDEWEB)

    Svejcar, J.; Vechet, S.; Pokluda, J. [Technical Univ. of Brno (Czech Republic). Faculty of Mechanical Engineering

    1997-12-31

    The paper summarizes the results of fatigue tests on austempered ductile iron. Attention is mainly focused on the effect of graphite on crack propagation and on some irregularities exhibited by ADI and other ductile irons, e.g., some specific features of fatigue fracture (especially the occurrence of fatigue striations on intergranular facets), decrease of fatigue limit with increasing UTS, and anomalous dependence of loading cycle amplitude on mean cycle stress.

  7. Fatigue behavior of dental resin composites: flexural fatigue in vitro versus 6 years in vivo

    NARCIS (Netherlands)

    Garcia-Godoy, F.; Frankenberger, R.; Lohbauer, U.; Feilzer, A.J.; Krämer, N.

    2012-01-01

    Objectives: To evaluate fatigue behavior of direct resin composite restorations (Tetric Ceram vs. Grandio) in vitro and in vivo over an observation period of 6 years. Methods: For the in vitro part, Young's moduli (YM) were calculated and both initial (FS: flexural strength) and fatigue flexural

  8. Fatigue behavior of dental resin composites: flexural fatigue in vitro versus 6 years in vivo

    NARCIS (Netherlands)

    F. Garcia-Godoy; R. Frankenberger; U. Lohbauer; A.J. Feilzer; N. Krämer

    2012-01-01

    Objectives: To evaluate fatigue behavior of direct resin composite restorations (Tetric Ceram vs. Grandio) in vitro and in vivo over an observation period of 6 years. Methods: For the in vitro part, Young's moduli (YM) were calculated and both initial (FS: flexural strength) and fatigue flexural str

  9. Superior Inhibitory Control and Resistance to Mental Fatigue in Professional Road Cyclists.

    Directory of Open Access Journals (Sweden)

    Kristy Martin

    Full Text Available Given the important role of the brain in regulating endurance performance, this comparative study sought to determine whether professional road cyclists have superior inhibitory control and resistance to mental fatigue compared to recreational road cyclists.After preliminary testing and familiarization, eleven professional and nine recreational road cyclists visited the lab on two occasions to complete a modified incongruent colour-word Stroop task (a cognitive task requiring inhibitory control for 30 min (mental exertion condition, or an easy cognitive task for 10 min (control condition in a randomized, counterbalanced cross-over order. After each cognitive task, participants completed a 20-min time trial on a cycle ergometer. During the time trial, heart rate, blood lactate concentration, and rating of perceived exertion (RPE were recorded.The professional cyclists completed more correct responses during the Stroop task than the recreational cyclists (705±68 vs 576±74, p = 0.001. During the time trial, the recreational cyclists produced a lower mean power output in the mental exertion condition compared to the control condition (216±33 vs 226±25 W, p = 0.014. There was no difference between conditions for the professional cyclists (323±42 vs 326±35 W, p = 0.502. Heart rate, blood lactate concentration, and RPE were not significantly different between the mental exertion and control conditions in both groups.The professional cyclists exhibited superior performance during the Stroop task which is indicative of stronger inhibitory control than the recreational cyclists. The professional cyclists also displayed a greater resistance to the negative effects of mental fatigue as demonstrated by no significant differences in perception of effort and time trial performance between the mental exertion and control conditions. These findings suggest that inhibitory control and resistance to mental fatigue may contribute to successful road cycling

  10. High temperature fatigue behavior of tungsten copper composites

    Science.gov (United States)

    Verrilli, M. J.; Kim, Y.-S.; Gabb, T. P.

    1990-01-01

    The present study investigates the high-temperature fatigue behavior of a 9-v/o tungsten fiber-reinforced copper matrix composite. Load-controlled isothermal fatigue at 260 and 560 C and thermomechanical fatigue (TMF) experiments, both in-phase and out-of-phase between 260 and 560 C, were performed. The stress-strain response under all conditions displayed considerable inelasticity. Strain ratchetting was observed during all the fatigue experiments. For the isothermal fatigue and in-phase TMF tests, the ratchetting was always in a tensile direction, continuing until failure. The ratchetting during the out-of-phase TMF test shifted from a tensile to a compressive direction. For all cases, the fatigue lives were found to be controlled by the damage of the copper matrix. On a stress basis, TMF loading substantially reduced lives relative to isothermal cycling.

  11. Localized bending fatigue behavior of high-strength steel monostrands

    DEFF Research Database (Denmark)

    Winkler, Jan; Fischer, Gregor; Georgakis, Christos T.

    2012-01-01

    In this paper, the localized bending fatigue behavior of pretensioned high strength steel monostrands is investigated. Furthermore, a new methodology using an optical photogrammetry system, which can quantify surface deformations on the strand is presented. The system allows measurement of the st......In this paper, the localized bending fatigue behavior of pretensioned high strength steel monostrands is investigated. Furthermore, a new methodology using an optical photogrammetry system, which can quantify surface deformations on the strand is presented. The system allows measurement...

  12. Deformation, fatigue and fracture behavior of two cast anisotropic superalloys

    Science.gov (United States)

    Milligan, Walter W.; Huron, Eric S.; Antolovich, Stephen D.

    1987-01-01

    Tensile and low cycle fatigue (LCF) tests were conducted on two cast anisotropic superalloys. The effects of temperature, strain rate and stress range were investigated. Deformation behavior was extensively characterized and modeled. LCF and fracture behavior were studied and correlated with deformation behavior.

  13. Fatigue Behavior for Composite Laminates with Circular Hole

    Institute of Scientific and Technical Information of China (English)

    Qi Hongyu; Wen Weidong; Sun Lianwen

    2004-01-01

    Based on the fatigue model of exponential function and WN criterion of static strength for the composite material laminates with a circular hole, the stress correct factorβ is presented. In order to gain the factorβ, the fatigue experiments of laminates with holes in different diameters and the same ratio of width and diameter. The fatigue behavior is usually accompanied with extensive damages. Those damages can affect composite materials in their strength and stiffness. The new model based on damage theory and strain equivalent hypothesis meets engineering requirement.T300/KH304, which is recently studied, is a high capability composite material. The fatigue analysis and tests of laminates with a hole in diameter of 5 mm are carried under difference stress levels. The simple, prompt and practical method was provided for the predication of fatigue life of composite material plate with a circular hole.

  14. Microstructure, Fatigue Behavior, and Failure Mechanisms of Direct Laser-Deposited Inconel 718

    Science.gov (United States)

    Johnson, Alex S.; Shao, Shuai; Shamsaei, Nima; Thompson, Scott M.; Bian, Linkan

    2017-03-01

    Inconel 718 is considered to be a superalloy with a series of superior properties such as high strength, creep resistance, and corrosion resistance at room and elevated temperatures. Additive manufacturing (AM) is particularly appealing to Inconel 718 because of its near-net-shape production capability for circumventing the poor machinability of this superalloy. Nevertheless, AM parts are prone to porosity, which is detrimental to their fatigue resistance. Thus, further understanding of their fatigue behavior is required before their widespread use in load-bearing applications. In this work, the microstructure and fatigue properties of AM Inconel 718, produced in a Laser Engineered Net Shaping (LENS™) system and heat treated with a standard heat treatment schedule, are evaluated at room temperature. Fully reversed strain controlled fatigue tests were performed on cylindrical specimens with straight gage sections at strain amplitudes ranging from 0.001 mm/mm to 0.01 mm/mm. The fracture surfaces of fatigue specimens were inspected with a scanning electron microscope. The results indicate that the employed heat treatment allowed the large, elongated grains and dendritic structure of the as-built material to break down into smaller, equiaxed grains, with some dendritic structures remaining between layers. The AM specimens were found to possess lower fatigue resistance than wrought Inconel 718, and this is primarily attributed to the presence of brittle metal-carbide/oxide inclusions or pores near their surface.

  15. Microstructure, Fatigue Behavior, and Failure Mechanisms of Direct Laser-Deposited Inconel 718

    Science.gov (United States)

    Johnson, Alex S.; Shao, Shuai; Shamsaei, Nima; Thompson, Scott M.; Bian, Linkan

    2016-12-01

    Inconel 718 is considered to be a superalloy with a series of superior properties such as high strength, creep resistance, and corrosion resistance at room and elevated temperatures. Additive manufacturing (AM) is particularly appealing to Inconel 718 because of its near-net-shape production capability for circumventing the poor machinability of this superalloy. Nevertheless, AM parts are prone to porosity, which is detrimental to their fatigue resistance. Thus, further understanding of their fatigue behavior is required before their widespread use in load-bearing applications. In this work, the microstructure and fatigue properties of AM Inconel 718, produced in a Laser Engineered Net Shaping (LENS™) system and heat treated with a standard heat treatment schedule, are evaluated at room temperature. Fully reversed strain controlled fatigue tests were performed on cylindrical specimens with straight gage sections at strain amplitudes ranging from 0.001 mm/mm to 0.01 mm/mm. The fracture surfaces of fatigue specimens were inspected with a scanning electron microscope. The results indicate that the employed heat treatment allowed the large, elongated grains and dendritic structure of the as-built material to break down into smaller, equiaxed grains, with some dendritic structures remaining between layers. The AM specimens were found to possess lower fatigue resistance than wrought Inconel 718, and this is primarily attributed to the presence of brittle metal-carbide/oxide inclusions or pores near their surface.

  16. Effect of Surface Nanocrystallization on Fatigue Behavior of Pure Titanium

    Science.gov (United States)

    Wang, Qi; Sun, Qiaoyan; Xiao, Lin; Sun, Jun

    2016-01-01

    The high-cycle fatigue behavior was investigated in pure titanium after surface nanocrystallization (SNC Ti). Compared with the coarse-grained titanium (CG Ti) samples, the SNC Ti samples exhibit an improved fatigue life. The SNC has a remarkable influence on the fatigue cracks initiation and growth of pure titanium. The results show that, because the free-surface cracking is suppressed by the surface nanogradient structure in the SNC Ti, the fatigue cracks initiation sites change from the free surface to the subsurface. Meanwhile, the fatigue crack growth rate decreases due to the microstructural feature and residual compressive stress. The deformation twins in the subsurface of SNC Ti have a marked effect on the fatigue crack initiation and the crack growth. The former effect is due to the twin boundaries being preferential sites for crack initiation, while the latter is associated with the barriers that the twin boundaries pose to the propagation of dislocations. Furthermore, microstructural analysis indicates that the dislocation distribution in SNC Ti gradually becomes homogenous as fatigue processes. This homogeneous microstructure is also beneficial to the improvement of fatigue life.

  17. Seismic Behavior of Fatigue-Retrofitted Steel Frame Piers

    Directory of Open Access Journals (Sweden)

    Kinoshita K.

    2013-01-01

    Full Text Available Fatigue retrofit works have been conducted on severely fatigue damaged beam-to-column connections of existing steel frame bridge piers in Japan. It is clear that retrofit works provides additional stiffness but the significance on the seismic behavior of steel frame piers is not clear. Since fatigue retrofit works have become prevalent, the effect of fatigue retrofit works on the seismic behavior of steel frame piers need to be understood. The objective of this study is therefore to investigate these effects of the retrofit work, especially installation of bolted splices, which is the most common technique. Elasto-plastic finite element earthquake response analyses were carried out. It is shown that the existence of bolted splices may increase seismic demand on the piers when plastic hinge zone is located on the beam. In addition, longer bolted splices using low yield strength steel are proposed to overcome this problem and are shown to give beneficial effects.

  18. Biaxial fatigue behavior of a powder metallurgical TRIP steel

    Directory of Open Access Journals (Sweden)

    S. Ackermann

    2015-10-01

    Full Text Available Multiaxial fatigue behavior is an important topic in critical structural components. In the present study the biaxial-planar fatigue behavior of a powder metallurgical TRIP steel (Transformation Induced Plasticity was studied by taking into account martensitic phase transformation and crack growth behavior. Biaxial cyclic deformation tests were carried out on a servo hydraulic biaxial tension-compression test rig using cruciform specimens. Different states of strain were studied by varying the strain ratio between the axial strain amplitudes in the range of -1 (shear loading to 1 (equibiaxial loading. The investigated loading conditions were proportional due to fixed directions of principal strains. The studied TRIP steel exhibits martensitic phase transformation from -austenite via ε-martensite into α‘- martensite which causes pronounced cyclic hardening. The α‘-martensite formation increased with increasing plastic strain amplitude. Shear loading promoted martensite formation and caused the highest α‘-martensite volume fractions at fatigue failure in comparison to uniaxial and other biaxial states of strain. Moreover, the fatigue lives of shear tests were higher than those of uniaxial and other biaxial tests. The von Mises equivalent strain hypothesis was found to be appropriate for uniaxial and biaxial fatigue, but too conservative for shear fatigue, according to literature for torsional fatigue. The COD strain amplitude which is based on crack opening displacement gave a better correlation of the investigated fatigue lives, especially those for shear loading. Different types of major cracks were observed on the sample surfaces after biaxial cyclic deformation by using electron monitoring in an electron beam universal system and scanning electron microscopy (SEM. Specimens with strain ratios of 1, 0.5, -0.1 and -0.5 showed mode I major cracks (perpendicular to the axis of maximum principal strain. Major cracks after shear fatigue

  19. Fatigue behavior of unirradiated V-5Cr-5Ti

    Energy Technology Data Exchange (ETDEWEB)

    Gieseke, B.G.; Stevens, C.O.; Grossbeck, M.L. [Oak Ridge National Lab., TN (United States)

    1995-04-01

    The objective of this research is to determine the low cycle fatigue behavior of V-5Cr-5Ti alloys for a range of temperatures and the extent of environmental effects at ambient temperatures. The results of in-vacuum low cycle fatigue tests are presented for unirradiated V-5Cr-5Ti tested at room temperature, 240, and 400{degree}C. A comparison of the fatigue data generated in rough and high vacuums shows that a pronounced environmental degradation of the fatiuge properties exists in this alloy at room temperature. Fatigue life was reduced by as much as 84%. Cyclic stress range data and SEM observations suggest that this reduction is due to a combination of increases in rates of crack initiation and subsequent growth. The relative contribution of each difference is dependent upon the strain range.

  20. Fatigue behavior of porous biomaterials manufactured using selective laser melting.

    Science.gov (United States)

    Yavari, S Amin; Wauthle, R; van der Stok, J; Riemslag, A C; Janssen, M; Mulier, M; Kruth, J P; Schrooten, J; Weinans, H; Zadpoor, A A

    2013-12-01

    Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4).

  1. Fatigue behavior of RC T-beams

    Directory of Open Access Journals (Sweden)

    Omar A. Farghal

    2014-09-01

    Full Text Available The objective of this research is to study the fatigue performance of reinforced concrete (RC T-beams strengthened in shear with Carbon Fiber Reinforced Polymer (CFRP composite. Experiments were conducted on RC beams with and without CFRP sheets bonded on their web surfaces and subjected to static and cycling loading. The obtained results showed that the strengthened beams could survive one million cycles of cyclic loading (=50% of maximum static load with no apparent signs of damage (premature failure demonstrating the effectiveness of CFRP strengthening system on extending the fatigue life of structures. Also, for beams having the same geometry, the applied strengthening technique can significantly enhance the cycling load particularly, in case of beams provided with U-jacket sheets. Moreover, although the failure mode for the different beams was a brittle one, the strengthened beams provided with U-jacket sheets approved an acceptable enhancement in the structural ductility.

  2. Fatigue Behavior and Deformation Mechanisms in Inconel 718 Superalloy Investigated

    Science.gov (United States)

    2005-01-01

    The nickel-base superalloy Inconel 718 (IN 718) is used as a structural material for a variety of components in the space shuttle main engine (SSME) and accounts for more than half of the total weight of this engine. IN 718 is the bill-of-material for the pressure vessels of nickel-hydrogen batteries for the space station. In the case of the space shuttle main engine, structural components are typically subjected to startup and shutdown load transients and occasional overloads in addition to high-frequency vibratory loads from routine operation. The nickel-hydrogen battery cells are prooftested before service and are subjected to fluctuating pressure loads during operation. In both of these applications, the structural material is subjected to a monotonic load initially, which is subsequently followed by fatigue. To assess the life of these structural components, it is necessary to determine the influence of a prior monotonic load on the subsequent fatigue life of the superalloy. An insight into the underlying deformation and damage mechanisms is also required to properly account for the interaction between the prior monotonic load and the subsequent fatigue loading. An experimental investigation was conducted to establish the effect of prior monotonic straining on the subsequent fatigue behavior of wrought, double-aged, IN 718 at room temperature. First, monotonic strain tests and fully-reversed, strain-controlled fatigue tests were conducted on uniform-gage-section IN 718 specimens. Next, fully reversed fatigue tests were conducted under strain control on specimens that were monotonically strained in tension. Results from this investigation indicated that prior monotonic straining reduced the fatigue resistance of the superalloy particularly at the lowest strain range. Some of the tested specimens were sectioned and examined by transmission electron microscopy to reveal typical microstructures as well as the active deformation and damage mechanisms under each of

  3. Fatigue Behavior of FDM Parts Manufactured with Ultem 9085

    Science.gov (United States)

    Fischer, Matthias; Schöppner, Volker

    2016-11-01

    The mechanical characterization of fused deposition modeling (FDM) parts is mostly done by static tests. In many applications, parts are also dynamically loaded. Here, fatigue tests can help to identify the expected lifetime of a part. This article discusses the fatigue behavior of FDM specimens manufactured with Ultem 9085. For this, tensile bars are manufactured according to ASTM D638 in different build orientations. Tests are performed in a range of pulsating tensile stresses, and S-N curves are documented for different build orientations. For higher loads, the FDM anisotropy characterizes the lifetime of used specimens, which is similar to static tensile bars. For lower loads, including a higher number of cycles to failure, S-N curves of different build orientations converge. In further tests, tensile bars were chemically smoothed with chloroform vapor. Chemical smoothing reduces surface roughness and increases tensile strength of specimens in the upright build direction. Fatigue tests of chemically treated specimens show no significant lifetime increase.

  4. Notch Corrosion Fatigue Behavior of Ti-6Al-4V

    Directory of Open Access Journals (Sweden)

    Sergio Baragetti

    2014-06-01

    Full Text Available The aim of this paper is to map the corrosion fatigue characteristics of Ti-6Al-4V alloy through the evaluation of the corrosion fatigue initiation and failure mechanisms. The study included the effect of the stress concentration factor at very high Kt values and the role of different inert or corrosive environments. This alloy is widely used in naval-structures and aero-engine communities and the outcomes of the work will have direct relevance to industrial service operations. Axial fatigue tests (R = 0.1; 2 × 105 cycles; f = 10 Hz were carried out on smooth and high notched (Ktmax = 18.65 flat specimens in laboratory air, paraffin oil, laboratory air + beeswax coating, recirculated 3.5% NaCl solution. The step loading procedure was used to perform the fatigue tests and the surface replica method and crack propagation gages were used to check crack nucleation and propagation until failure. Log-Log plots of σmax vs. Kt showed a bilinear behavior and enabled the demonstration of the presence of a threshold stress intensity factor (Kt = 8–9, after which the environment has no effect on the fatigue damage for all the tested environments.

  5. Notch Corrosion Fatigue Behavior of Ti-6Al-4V.

    Science.gov (United States)

    Baragetti, Sergio

    2014-06-11

    The aim of this paper is to map the corrosion fatigue characteristics of Ti-6Al-4V alloy through the evaluation of the corrosion fatigue initiation and failure mechanisms. The study included the effect of the stress concentration factor at very high Kt values and the role of different inert or corrosive environments. This alloy is widely used in naval-structures and aero-engine communities and the outcomes of the work will have direct relevance to industrial service operations. Axial fatigue tests (R = 0.1; 2 × 10⁵ cycles; f = 10 Hz) were carried out on smooth and high notched (Ktmax = 18.65) flat specimens in laboratory air, paraffin oil, laboratory air + beeswax coating, recirculated 3.5% NaCl solution. The step loading procedure was used to perform the fatigue tests and the surface replica method and crack propagation gages were used to check crack nucleation and propagation until failure. Log-Log plots of σmaxvs.Kt showed a bilinear behavior and enabled the demonstration of the presence of a threshold stress intensity factor (Kt = 8-9), after which the environment has no effect on the fatigue damage for all the tested environments.

  6. High-cycle Fatigue Fracture Behavior of Ultrahigh Strength Steels

    Institute of Scientific and Technical Information of China (English)

    Weijun HUI; Yihong NIE; Han DONG; Yuqing WENG; Chunxu WANG

    2008-01-01

    The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy (FESEM). It was found that the size of inclusion has significant effect on the fatigue behavior.For AISI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curvedisplays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 μm. In the case of internal inclusion-induced fractures at cycles beyond about 1×106 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet (GBF) was observed in the vicinity around the inclusion. The GBF sizes increasewith increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×106. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.

  7. INVESTIGATION OF THE LOW-CYCLE FATIGUE AND FATIGUE CRACK GROWTH BEHAVIORS OF P91 BASE METAL AND WELD JOINTS

    Institute of Scientific and Technical Information of China (English)

    H.C. Yang; Y. Tu; M.M. Yu; J. Zhao

    2004-01-01

    Low cycle fatigue tests and crack growth propagations tests on P91 pipe base metal and its weld joints were conducted at three different temperatures: room temperature,550℃ and 575℃. The strain-life was analyzed, and the changes in fatigue life behavior and fatigue growth rates with increasing temperature were discussed. The different properties of the base metal and its weld joint have been analyzed.

  8. Fatigue Crack Propagation Behavior of Rubber-toughened Epoxy Resin

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Fatigue crack propagation (FCP) behaviors of mass fraction 15% CTBN (carboxyl-terminated butadiene-acrylonitrile), 15% Qishi toughening-agent toughened anhydride-cured epoxy resins (EP), and pure anhydride-cured EP were measured. The results showed that the two main toughening mechanisms, localized shear yielding and void plastics growth, which occurred near the threshold region because the rubber size is much less than the plastics size at the crack front, improved the near threshold FCP behavior and increased the threshold. The stable FCP behavior was obviously improved with the FCP rates decreased to less than 21%.

  9. Environmental fatigue behaviors of wrought and cast stainless steels in 310 .deg. C Deoxygenated Water

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Pyung Yeon

    2011-02-15

    Environmental fatigue behaviors of wrought type 316LN stainless steel and cast CF8M stainless steel were investigated. LCF tests were performed at fixed strain rate of 0.04%/s with 0.4%, 0.6%, 0.8%, 1.0% strain amplitudes in 310 .deg. C deoxygenated water environment. In addition, to analyze microstructure effect on fatigue behavior, low cycle fatigue tests in air environment were performed at fixed strain rate of 0.4%/s, 0.04%/s with 0.4%, 0.8% strain amplitudes. It was shown that the low cycle fatigue life of CF8M in a 310 .deg. C deoxygenated water environment was slightly longer than that of 316LN. On the other hand, the low cycle fatigue life of CF8M in a 310 .deg. C air environment was slightly shorter than that of 316LN or was similar with that of 316LN. Through OM observation and phase image analysis, it was confirmed that the ferrite content of CF8M tested in a 310 .deg. C deoxygenated water environment was larger than that of CF8M tested in a 310 .deg. C air environment. It was shown that the ferrite phase fraction of CF8M tested in 310 .deg. C deoxygenated water environment was approximately 26∼28% and that of CF8M tested in air environment was approximately 10∼12%. The difference of ferrite content in CF8M results in superior tensile properties as higher ferrite content. Furthermore, the difference of ferrite content in CF8M might be the cause of different result of fatigue life between CF8M and 316LN depending on environment. In this study, focused on CF8M having 26∼28% ferrite content, to understand the causes of these differences in a 310 .deg. C deoxygenated water environment, fracture surface and crack morphology were observed. And material factors like microstructure, mechanical properties factors like stress behavior during fatigue life, factors by environmentally assisted cracking (EAC) like hydrogen induced cracking (HIC) and chemical compositions of both materials were analyzed. Mainly in a 310 .deg. C deoxygenated water environment, the

  10. Influence of Nickel Particle Reinforcement on Cyclic Fatigue and Final Fracture Behavior of a Magnesium Alloy Composite

    Directory of Open Access Journals (Sweden)

    Manoj Gupta

    2012-06-01

    Full Text Available The microstructure, tensile properties, cyclic stress amplitude fatigue response and final fracture behavior of a magnesium alloy, denoted as AZ31, discontinuously reinforced with nano-particulates of aluminum oxide and micron size nickel particles is presented and discussed. The tensile properties, high cycle fatigue and final fracture behavior of the discontinuously reinforced magnesium alloy are compared with the unreinforced counterpart (AZ31. The elastic modulus and yield strength of the dual particle reinforced magnesium alloy is marginally higher than of the unreinforced counterpart. However, the tensile strength of the composite is lower than the monolithic counterpart. The ductility quantified by elongation to failure over 0.5 inch (12.7 mm gage length of the test specimen showed minimal difference while the reduction in specimen cross-section area of the composite is higher than that of the monolithic counterpart. At the microscopic level, cyclic fatigue fractures of both the composite and the monolithic alloy clearly revealed features indicative of the occurrence of locally ductile and brittle mechanisms. Over the range of maximum stress and at two different load ratios the cyclic fatigue resistance of the magnesium alloy composite is superior to the monolithic counterpart. The mechanisms responsible for improved cyclic fatigue life and resultant fracture behavior of the composite microstructure are highlighted.

  11. Rapid Assessment of the Role of Microstructural Variability in the Fatigue Behavior of Structural Alloys using Ultrasonic Fatigue

    Science.gov (United States)

    2007-06-23

    649. References 17. Q.C. Wang, D. Apelian, D.A. Lados, "Fatigue behavior of A356 -T6 aluminum cast alloys. Part 1: Effect of casting defects", I. J...Apelian, D.A. Lados, "Fatigue behavior of 2. R.E. Little, E.H. Jebe, Statistical Design of Fatigue A356 -T6 aluminum cast alloys. Part II: Effect of...einforced aluminum alloy, 2009AVI15SiCp, where clustering of SiC particles and the presence of processing-related inclusions is expected to contri

  12. Fatigue behavior of the magnesium alloy ZK60 in high cycle fatigue

    NARCIS (Netherlands)

    Constantinescu, D.M.; Moldovan, P.; Sillekens, W.H.; Sandu, M.; Apostol, D.A.; Miron, M.C.

    2009-01-01

    Not too much information is available in the literature for establishing fatigue properties of magnesium alloys. A compilation of existing fatigue and fatigue crack growth data of different Mg-alloys has been published by ASM International. One can underline that fatigue properties of some of the st

  13. Effect of Phosphate-Buffered Solution Corrosion on the Ratcheting Fatigue Behavior of a Duplex Mg-Li-Al Alloy

    Science.gov (United States)

    Yuan, Xin; Yu, Dunji; Gao, Li-Lan; Gao, Hong

    2016-05-01

    This work reports the uniaxial ratcheting and fatigue behavior of a duplex Mg-Li-Al alloy under the influence of phosphate-buffered solution corrosion. Microstructural observations reveal pitting and filament corrosion defects, which impair the load-bearing capacity of the alloy and cause stress concentration, thus leading to an accelerated accumulation of ratcheting strain and shortened fatigue life under the same nominal loading conditions. Comparing Smith model, Smith-Watson-Topper model, and Paul-Sivaprasad-Dhar model, a ratcheting fatigue life prediction model based on the Broberg damage rule and the Paul-Sivaprasad-Dhar model was proposed, and the model yielded a superior prediction for the studied magnesium alloy.

  14. A coach in your pocket: on chronic cancer-related fatigue and physical behavior

    NARCIS (Netherlands)

    Wolvers, Maria Dorethea Jacoba

    2017-01-01

    Fatigue is a common and distressing long-term consequence of cancer. Chronic cancer-related fatigue affects work ability, hampers in maintaining social relations, and impacts patients’ well-being. Most treatments for chronic cancer-related fatigue focus to some extend on changing physical behavior,

  15. HIGH-TEMPERATURE LOW CYCLE FATIGUE BEHAVIOR OFNICKEL BASE SUPERALLOY GH536

    Institute of Scientific and Technical Information of China (English)

    M. Zhao; L.Y. Xu; K.S. Zhang; B.Y. Yang

    2001-01-01

    Low cycle fatigue tests on nickel base superalloy GH536 were performed at 600. 700and 800°C. The strain-life and cyclic stress-strain relationship were given at various temperatures. The change in fatigue life behavior and fatigue parameters with temperature increasing was discussed. At low and intermediate total strain amplitudes,the fatigue life was found to decrease with increasing temperature.``

  16. Effect of Heat Treatment Process on Microstructure and Fatigue Behavior of a Nickel-Base Superalloy

    Directory of Open Access Journals (Sweden)

    Peng Zhang

    2015-09-01

    Full Text Available The study of fatigue behaviors for nickel-base superalloys is very significant because fatigue damage results in serious consequences. In this paper, two kinds of heat treatment procedures (Pro.I and Pro.II were taken to investigate the effect of heat treatment on microstructures and fatigue behaviors of a nickel-base superalloy. Fatigue behaviors were studied through total strain controlled mode at 650 °C. Manson-Coffin relationship and three-parameter power function were used to predict fatigue life. A good link between the cyclic/fatigue behavior and microscopic studies was established. The cyclic deformation mechanism and fatigue mechanism were discussed. The results show that the fatigue resistance significantly drops with the increase of total strain amplitudes. Manson-Coffin relationship can well predict the fatigue life for total strain amplitude from 0.5% to 0.8%. The fatigue resistance is related with heat treatment procedures. The fatigue resistance performance of Pro.I is better than that of Pro.II. The cyclic stress response behaviors are closely related to the changes of the strain amplitudes. The peak stress of the alloy gradually increases with the increase of total strain amplitudes. The main fracture mechanism is inhomogeneous deformation and the different interactions between dislocations and γ′ precipitates.

  17. The influence of cell morphology on the compressive fatigue behavior of Ti-6Al-4V meshes fabricated by electron beam melting.

    Science.gov (United States)

    Zhao, S; Li, S J; Hou, W T; Hao, Y L; Yang, R; Misra, R D K

    2016-06-01

    Additive manufacturing technique is a promising approach for fabricating cellular bone substitutes such as trabecular and cortical bones because of the ability to adjust process parameters to fabricate different shapes and inner structures. Considering the long term safe application in human body, the metallic cellular implants are expected to exhibit superior fatigue property. The objective of the study was to study the influence of cell shape on the compressive fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting. The results indicated that the underlying fatigue mechanism for the three kinds of meshes (cubic, G7 and rhombic dodecahedron) is the interaction of cyclic ratcheting and fatigue crack growth on the struts, which is closely related to cumulative effect of buckling and bending deformation of the strut. By increasing the buckling deformation on the struts through cell shape design, the cyclic ratcheting rate of the meshes during cyclic deformation was decreased and accordingly, the compressive fatigue strength was increased. With increasing bending deformation of struts, fatigue crack growth in struts contributed more to the fatigue damage of meshes. Rough surface and pores contained in the struts significantly deteriorated the compressive fatigue strength of the struts. By optimizing the buckling and bending deformation through cell shape design, Ti-6Al-4V alloy cellular solids with high fatigue strength and low modulus can be fabricated by the EBM technique. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. The concept of fatigue fracture toughness in fatigue delamination growth behavior

    NARCIS (Netherlands)

    Yao, L.; Alderliesten, R.C.; Benedictus, R.

    2015-01-01

    This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed t

  19. Low cycle fatigue behavior of high strength gun steels

    Institute of Scientific and Technical Information of China (English)

    Maoqiu Wang; Han Dong; Qi Wang; Changgang Fan

    2004-01-01

    The low cycle fatigue (LCF) behavior of two high strength steels, with nominal chemical compositions (mass fraction, %)of 0.40C-1.5Cr-3Ni-0.4Mo-0.2V (PCrNi3MoV) and 0.25C-3Cr-3Mo-0.8Ni-0.1Nb (25Cr3Mo3NiNb), was investigated by using the smooth bar specimens subjected to strained-controlled push-pull loading. It is found that both steels show cyclic softening, but 25Cr3Mo3NiNb steel has a lower tendency to cyclic softening. 25Cr3Mo3NiNb steel has higher fatigue ductility, and its transition fatigue life is almost three times that of PCrNi3MoV. 25Cr3Mo3NiNb steel also shows higher LCF life either at a given total strain amplitude above 0.5% or at any given plastic strain amplitude, despite its lower monotonic tensile strength than that of PCrNi3MoV.It also means that 25Cr3Mo3NiNb steel can endure higher total strain amplitude and plastic strain amplitude at a given number of reversals to failure within 104. 25Cr3Mo3NiNb steel is expected to be a good gun steel with high LCF properties because only several thousand firings are required for gun barrel in most cases.

  20. Isothermal and nonisothermal fatigue behavior of a metal matrix composite

    Science.gov (United States)

    Gabb, T. P.; Gayda, J.; Mackay, R. A.

    1990-01-01

    The isothermal and nonisothermal fatigue resistance of a metal matrix composite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 vol pct continuous SiC fibers was investigated. The fibers were nominally oriented parallel to the specimen axis. Isothermal fatigue tests were performed in air at 300 and 550 C. The MMC had good isothermal fatigue resistance at low cyclic stress, with fatigue cracks initiating from fiber-matrix interfaces and foil laminations. At high cyclic stresses, stress relaxation in the matrix reduced isothermal composite fatigue resistance at 550 C. Nonisothermal fatigue loading substantially degraded composite fatigue resistnce. This degradation was produced by a thermomechanical fatigue damage mechanism associated with the fiber-matrix interfaces.

  1. Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

    Institute of Scientific and Technical Information of China (English)

    SI Tingzhi; LIU Ning; ZHANG Qingan; YOU Xianqing

    2008-01-01

    The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt. % TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δα). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.

  2. Fatigue and environmental behavior of long fiber thermoplastic (LFT) composites

    Science.gov (United States)

    Goel, Ashutosh

    In the present work we have characterized the mechanical behavior of long fiber thermoplastic (LFT) composites (21% E-glass fiber/polypropylene) under different conditions. We start by comparing the elastic modulus of LFT predicted by a microstructure-based approach called Object Oriented Finite (OOF) element method, and compare the result with prediction from various models commonly used in the literature and the experimental value. The predictions from the models used currently in the literature did not agree well with the experimental value due to the assumptions inherent in the models. The prediction by OOF was the closest to the experimental value because of the microstructure based approach which takes into account the fiber distribution and orientation during the finite element calculation. This was followed by characterization of fatigue behavior of LFT. Samples tested along longitudinal direction showed a higher fatigue life than the transverse samples because of the preferred orientation of the fibers along the longitudinal direction developed during the processing of LFT by extrusion-compression molding process. Fatigue life decreased with increase in frequency. Hysteretic energy loss and temperature rise were measured; they depended on the stress amplitude as well as the cyclic frequency. LFT composite showed a lower temperature rise compared to neat PP because LFT has higher thermal conductivity than neat PP and thus faster heat dissipation to the surroundings occur. The hysteretic heating also led to decrease in the modulus of LFT as a function of number of cycles. The last part of the work was to study the effect of ultraviolet (UV) exposure on the microstructure and mechanical properties of LFT. Microscopic observations revealed that the damage due to UV was confined only to the surface region in the form of surface cracking and exposure of fibers to the surface in the case of LFT. FTIR and nanoindentation results showed that there was a large

  3. Deformation and fatigue behaviors of carburized automotive gear steel and predictions

    Directory of Open Access Journals (Sweden)

    Bonglae Jo

    2016-07-01

    Full Text Available The fatigue behavior of carburized components such as automotive transmission gears is very complex due to hardness and microstructure difference, residual stresses and multi-axial stress states developed between the case and the core. In addition, automotive gears in service, commonly used in helical type, are actually subjected to complex stress conditions such as bending, torsion, and contact stress states. This study presents experimental and analytical results on deformation behavior of carburized steels, widely used in automotive gears, under cyclic stress conditions including axial and torsion loadings. Axial fatigue tests and rotating bending fatigue tests are also included. Predictions of cyclic deformation and fatigue behaviors of the carburized steel with two-layer model are compared with experimental results. The carburized steel investigated in this study exhibited cyclic softening under both axial loading and torsional loading. Predicted results with simple two-layer model for the cyclic deformation and fatigue behaviors were comparatively similar to the experimental data.

  4. Laminate Analyses, Micromechanical Creep Response, and Fatigue Behavior of Polymer Matrix Composite Materials.

    Science.gov (United States)

    1982-12-01

    FATIGUE BEHAVIOR of POLYMER MATRIX COMPOSITE MATERIALS , 4 " .’* .. . . ". ... .. ... . . ~December 1982 41 .. FINAL REPORT .Army Research Office I I...DEPARTMENT REPORT UWME-DR-201-108-1 LAMINATE ANALYSES, MICROMECHANICAL CREEP RESPONSE, AND FATIGUE BEHAVIOR OF POLYMER MATRIX COMPOSITE MATERIALS...Behavior of Polymer Matrix Composite 16 Sept. 1979 - 30 Nov. 1982 Materials 6 PERFORMING ORG. REPORT NUMBER UWME-DR-201-108-1 7. AUTHOR(.) S. CONTRACT

  5. Effect of shot peening process on fatigue behavior of an alloyed austempered ductile iron

    Directory of Open Access Journals (Sweden)

    Amir Sadighzadeh Benam

    2011-08-01

    Full Text Available Shot peening is one of the most common surface treatments to improve the fatigue behavior of metallic parts. In this study the effect of shot peening process on the fatigue behavior of an alloyed austempered ductile iron (ADI has been studied. Austempering heat treatment consisted of austenitizing at 875℃ for 90 min followed by austempering at three different temperatures of 320, 365 and 400℃. Rotating-bending fatigue test was carried out on samples after shot peening by 0.4 – 0.6 mm shots. XRD and SEM analysis, micro hardness and roughness tests were carried out to study the fatigue behavior of the samples. Results indicate that the fatigue strengths of samples austempered at 320, 365 and 400℃ are increased by 27.3%, 33.3% and 48.4%, respectively, after shot peening process.

  6. Fatigue behavior of lubricated Ni-Ti endodontic rotary instruments

    Directory of Open Access Journals (Sweden)

    A. Brotzu

    2014-04-01

    Full Text Available The use of Ni-Ti alloys in the practice of endodontic comes from their important properties such as shape memory and superelasticity phenomena, good corrosion resistance and high compatibility with biological tissues. In the last twenty years a great variety of nickel-titanium rotary instruments, with various sections and taper, have been developed and marketed. Although they have many advantages and despite their increasing popularity, a major concern with the use of Ni-Ti rotary instruments is the possibility of unexpected failure in use due to several reasons: novice operator handling, presence manufacturing defects, fatigue etc. Recently, the use of an aqueous gel during experimental tests showed a longer duration of the instruments. The aim of the present work is to contribute to the study of the fracture behavior of these endodontic rotary instruments particularly assessing whether the use of the aqueous lubricant gel can extend their operative life stating its reasons. A finite element model (FEM has been developed to support the experimental results. The results were rather contradictory, also because the Perspex (Poly-methyl methacrylate, PMMA cannot simulate completely the dentin mechanical behavior; however the results highlight some interesting points which are discussed in the paper.

  7. The process of change in pain during cognitive-behavior therapy for chronic fatigue syndrome.

    NARCIS (Netherlands)

    Bloot, L.; Heins, M.J.; Donders, R.; Bleijenberg, G.; Knoop, H.

    2015-01-01

    Background: Cognitive-behavior therapy (CBT) leads to a reduction of fatigue and pain in chronic fatigue syndrome. The processes underlying the reduction in pain have not been investigated. Recently, it was shown that increased self-efficacy, decreased focusing on symptoms, increased physical

  8. The Process of Change in Pain During Cognitive-Behavior Therapy for Chronic Fatigue Syndrome

    NARCIS (Netherlands)

    Bloot, L.; Heins, M.J.; Donders, R.; Bleijenberg, G.; Knoop, H.

    2015-01-01

    BACKGROUND: Cognitive-behavior therapy (CBT) leads to a reduction of fatigue and pain in chronic fatigue syndrome. The processes underlying the reduction in pain have not been investigated. Recently, it was shown that increased self-efficacy, decreased focusing on symptoms, increased physical

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

    Energy Technology Data Exchange (ETDEWEB)

    Warren, A.S.

    1990-01-01

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

  10. Effects of recrystallization on the low cycle fatigue behavior of directionally solidified superalloy DZ40M

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yang; WANG Lei; LI Hongyun; YU Teng; LIU Yang

    2008-01-01

    The effects of recrystallization on low cycle fatigue behavior were investigated on directionally solidified Co-base superalloy DZAOM.Optical microscopy and SEM were used to examine the mierostructure and fracture surface of the specimens.The mechanical testing results demonstrated that the low cycle fatigue property of DZ40M significantly decreased with the partial reerystallization.Fatigue cracks initiate near the carbides and the grain boundaries with slip-bands.Both the fatigue crack initiation and propagation can be accelerated with the occurrences of recrystallized grain boundaries.

  11. Influence of neodymium on high cycle fatigue behavior of die cast AZ91D magnesium alloy

    Institute of Scientific and Technical Information of China (English)

    杨友; 李雪松

    2010-01-01

    High cycle fatigue behavior of die cast AZ91D magnesium alloy with different Nd contents was investigated.Axial mechanical fatigue tests were conducted at the stress ratio R=0.1 and the fatigue strength was evaluated using up-to-down load method on specimens of AZ91D with different Nd contents.The results showed that the grain of AZ91D alloy was refined,the size and amount of β-Mg17Al12 phase decreased and distributed uniformly with increasing Nd content.At the number of cycles to failure,Nf=107,the fatigue...

  12. Fatigue behavior of carbon/epoxy composites reinforced with 3-Dimensional woven fabric

    Directory of Open Access Journals (Sweden)

    Mehmet Karahan

    2013-07-01

    Full Text Available This paper reports results of study of fatigue behavior of a non-crimp 3-dimensional woven carbon/epoxy composite in tension-tension fatigue. Infinite fatigue life limit corresponds to the load of 27.5 kN for fill direction. The damage under fatigue loading starts and develops from intersection of z-yarns and fill yarns. Since the z-yarns bonded the yarn layers, it is not seen the delaminastion damages. This indicate that for load carrying capacity and stiffness of 3-dimensional composites better than classic 2-dimensional textile composites.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-08-20

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

  14. Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel

    Science.gov (United States)

    Sarkar, Aritra; Vijayanand, V. D.; Parameswaran, P.; Shankar, Vani; Sandhya, R.; Laha, K.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2014-06-01

    Creep tests were carried out at 823 K (550 °C) and 210 MPa on Reduced Activation Ferritic-Martensitic (RAFM) steel which was subjected to different extents of prior fatigue exposure at 823 K at a strain amplitude of ±0.6 pct to assess the effect of prior fatigue exposure on creep behavior. Extensive cyclic softening that characterized the fatigue damage was found to be immensely deleterious for creep strength of the tempered martensitic steel. Creep rupture life was reduced to 60 pct of that of the virgin steel when the steel was exposed to as low as 1 pct of fatigue life. However, creep life saturated after fatigue exposure of 40 pct. Increase in minimum creep rate and decrease in creep rupture ductility with a saturating trend were observed with prior fatigue exposures. To substantiate these findings, detailed transmission electron microscopy studies were carried out on the steel. With fatigue exposures, extensive recovery of martensitic-lath structure was distinctly observed which supported the cyclic softening behavior that was introduced due to prior fatigue. Consequently, prior fatigue exposures were considered responsible for decrease in creep ductility and associated reduction in the creep rupture strength.

  15. Effects of fine porosity on the fatigue behavior of a powder metallurgy superalloy

    Science.gov (United States)

    Miner, R. V.; Dreshfield, R. L.

    1980-01-01

    Hot-isostatically-pressed powder-metallurgy Astroloy was obtained which contained 1.4 percent porosity at the grain boundaries produced by argon entering the powder container during pressing. This material was tested at 650 C in fatigue, creep-fatigue, tension, and stress-rupture and the results compared with data on sound Astroloy. They influenced fatigue crack initiation and produced a more intergranular mode of propagation but fatigue life was not drastically reduced. Fatigue behavior of the porous material showed typical correlation with tensile behavior. The plastic strain range-life relation was reduced proportionately with the reduction in tensile ductility, but the elastic strain range-life relation was changed little.

  16. Ratcheting fatigue behavior of Zircaloy-2 at room temperature

    Science.gov (United States)

    Rajpurohit, R. S.; Sudhakar Rao, G.; Chattopadhyay, K.; Santhi Srinivas, N. C.; Singh, Vakil

    2016-08-01

    Nuclear core components of zirconium alloys experience asymmetric stress or strain cycling during service which leads to plastic strain accumulation and drastic reduction in fatigue life as well as dimensional instability of the component. Variables like loading rate, mean stress, and stress amplitude affect the influence of asymmetric loading. In the present investigation asymmetric stress controlled fatigue tests were conducted with mean stress from 80 to 150 MPa, stress amplitude from 270 to 340 MPa and stress rate from 30 to 750 MPa/s to study the process of plastic strain accumulation and its effect on fatigue life of Zircaloy-2 at room temperature. It was observed that with increase in mean stress and stress amplitude accumulation of ratcheting strain was increased and fatigue life was reduced. However, increase in stress rate led to improvement in fatigue life due to less accumulation of ratcheting strain.

  17. The Fatigue Behavior of Steel Structures under Random Loading

    DEFF Research Database (Denmark)

    Agerskov, Henning

    2009-01-01

    of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests......Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part...... and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude...

  18. The Fatigue Behavior of Steel Structures under Random Loading

    DEFF Research Database (Denmark)

    Agerskov, Henning

    2008-01-01

    of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests......Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part...... and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude...

  19. The effect of microstructure on the fatigue behavior of Ni base superalloys

    Science.gov (United States)

    Antolovich, S. D.; Jayaraman, N.

    1983-01-01

    Nickel-base superalloys are used in jet engine components such as disks, turbine blades, and vanes. Improvements in the fatigue behavior will allow the life to be extended or the payloads to be increased. The first part of the present investigation deals primarily with the effects of microstructural variations on the fatigue crack propagation (FCP) behavior of nickel-base alloys, while the second part is concerned with low-cycle fatigue (LCF) behavior of Ni base systems. Waspaloy at low temperature is considered, taking into account material heat treatment and test procedures, a composite plot of Waspaloy FCP data, Paris law fatigue crack propagation constants, monotonic tensile data, and overload FCP test results for Waspaloy. It is found that the FCP and overload behavior of nickel-base alloys may be markedly improved by heat treating. Attention is given to effects of cyclic deformation on microstructure and substructure, environmental damage, and an environmental/deformation model of high temperature LCF.

  20. Study of fatigue behavior of longitudinal welded pipes

    Science.gov (United States)

    Simion, P.; Dia, V.; Istrate, B.; Hrituleac, G.; Hrituleac, I.; Munteanu, C.

    2016-08-01

    During transport and storage of the various fluids, welded pipes are subjected to cyclic loading due to pressure fluctuations that often exceed the prescribed values for normal operation. These cyclic loading can significantly reduce the life of the pipes; as a result the design should be based on the fatigue strength not only on static resistance. In general the fatigue strength of pipes is dependent by strength, pipe geometry and surface quality. In case of the electric longitudinal welded pipes, the fatigue strength is significantly limited by concentration of residual stress and the size of existing defects in the weld seam. This paper presents the fatigue behaviour of the electric welded pipes by high frequency, under conditions that simulate real operating conditions pipes. Fatigue testing was performed on welded pipes made of micro alloyed carbon steels. Some of these pipes were previously subjected to a heat treatment of normalization, in order to also determine the influence of heat treatment on the fatigue strength of welded pipes. To determine and correlate the different factors affecting the fatigue strength, welded pipes were also subjected to various tests: tensile tests, impact tests, measurement of micro hardness, microstructural analysis by optical microscopy and scanning electron microscopy.

  1. Low cycle fatigue behavior of aluminum/stainless steel composites

    Science.gov (United States)

    Bhagat, R. B.

    1983-01-01

    Composites consisting of an aluminum matrix reinforced with various volume fractions of stainless steel wire were fabricated by hot die pressing under various conditions of temperature, time, and pressure. The composites were tested in plane bending to complete fracture under cycle loading, and the results were analyzed on a computer to obtain a statistically valid mathematical relationship between the low-cycle fatigue life and the fiber volume fraction of the composite. The fractured surfaces of the composites were examined by scanning electron microscopy to identify the characteristic features of fatigue damage. Fatigue damage mechanisms are proposed and discussed.

  2. Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Zargarian, A.; Esfahanian, M. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kadkhodapour, J., E-mail: j.kad@srttu.edu [Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Stuttgart (Germany); Ziaei-Rad, S. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)

    2016-03-01

    In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1–0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. - Highlights: • Numerical simulation was used to predict fatigue behavior of titanium scaffolds. • Good agreement between numerical and experimental results • S–N curves obeyed the power law. • Fatigue strength of scaffolds was proportional to their Young's modulus. • Failure surface of scaffolds was inclined at an angle of 45° to loading.

  3. Room temperature fatigue behavior of OFHC copper and CuAl25 specimens of two sizes

    DEFF Research Database (Denmark)

    Singhal, A.; Stubbins, J.F.; Singh, B.N.

    1994-01-01

    requiring an understanding of their fatigue behavior.This paper describes the room temperature fatigue behavior of unirradiated OFHC (oxygen-free high-conductivity) copper and CuAl25 (copper strengthened with a 0.25% atom fraction dispersion of alumina). The response of two fatigue specimen sizes to strain......Copper and its alloys are appealing for application in fusion reactor systems for high heat flux components where high thermal conductivities are critical, for instance, in divertor components. The thermal and mechanical loading of such components will be, at least in part, cyclic in nature, thus...... controlled fatigue loading is examined, and differences in behavior are discussed. Specimens with the smaller size are now being irradiated in several reactors...

  4. Flexural Fatigue Behavior of Polypropylene Fiber Reinforeed Segment Conerete

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The influence of polypropylene fiber on the flexural fatigue performance of high- strength concrete (HSC), which could be used as cover of reinforcement of segment, was investigate by three-point load bending tests. Also, the flexural fatigue equations of high-strength concrete with and without polypropylene fiber were established through test analysis. The experimental results indicate that the addition of polypropylene fiber can improve the static bending strength of segment concrete, and the important is that it can markedly increase the flexural fatigue performance of the HSC subjected to cyclic bending load. Especially when with 1.37 kg/m3 addition of the fiber was corporate with silica fume and slag powder, the fatigue life of the HSC can be increased by 43.4% compared to that of the segment concrete without fiber,silica fume and slag.

  5. Magnetomechanical behavior for assessment of fatigue process in ferromagnetic steel

    Science.gov (United States)

    Bao, S.; Gong, S. F.

    2012-12-01

    In this work, the change of magnetization as a function of applied stress has been investigated for test specimens of AISI 1018 steel. The various stages of fatigue damage process are characterized by the magnetomechanical measurements recorded by an APS 428D fluxgate magnetometer. Of great significance is the fact that the stress-magnetic field hysteresis loop area changes systematically with the progression of fatigue. The magnetomechanical hysteresis demonstrates conspicuous changes in the initial stage of fatigue loading, then reverts to a relatively stable phase, and finally, drastic variations appear again as the cyclic loadings approach terminal failure. This work demonstrated that it is possible to correlate the progress of fatigue in ferromagnetic steels with the nondestructive evaluation technique of the magnetomechanical effect.

  6. Analysis of the cyclic behavior and fatigue damage of extruded AA2017 aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    May, A., E-mail: abdelghani1980@yahoo.fr [INSA/GPM, CNRS UMR 6634, BP 08 avenue de l' université, 76801 Saint Etienne du Rouvray Cedex (France); Laboratoire Génie des Matériaux, Ecole Militaire Polytechnique, BP 17 Bordj El-Bahri Algiers (Algeria); Taleb, L., E-mail: lakhdar.taleb@insa-rouen.fr [INSA/GPM, CNRS UMR 6634, BP 08 avenue de l' université, 76801 Saint Etienne du Rouvray Cedex (France); Belouchrani, M.A., E-mail: nbelouch@yahoo.fr [Laboratoire Génie des Matériaux, Ecole Militaire Polytechnique, BP 17 Bordj El-Bahri Algiers (Algeria)

    2013-06-01

    The present work is devoted to study the anisotropic behavior of an extruded aluminum alloy under cyclic loading in axial and shear directions. In first, we have studied its elastoplastic behavior through the evolution of stress–strain loops, isotropic and kinematic hardening and we have associated this behavior with the evolution of its elastic adaptation (shakedown). In second, we have studied the behavior of the material in fatigue damage using the evolution of stiffness. Finally, microstructural investigations were performed on fractured surfaces using scanning electron microscope (SEM) in order to understand the evolution of fatigue damage during cyclic loading.

  7. The Corrosion and Corrosion Fatigue Behavior of Nickel Based Alloy Weld Overlay and Coextruded Claddings

    Science.gov (United States)

    Stockdale, Andrew

    The use of low NOx boilers in coal fired power plants has resulted in sulfidizing corrosive conditions within the boilers and a reduction in the service lifetime of the waterwall tubes. As a solution to this problem, Ni-based weld overlays are used to provide the necessary corrosion resistance however; they are susceptible to corrosion fatigue. There are several metallurgical factors which give rise to corrosion fatigue that are associated with the localized melting and solidification of the weld overlay process. Coextruded coatings offer the potential for improved corrosion fatigue resistance since coextrusion is a solid state coating process. The corrosion and corrosion fatigue behavior of alloy 622 weld overlays and coextruded claddings was investigated using a Gleeble thermo-mechanical simulator retrofitted with a retort. The experiments were conducted at a constant temperature of 600°C using a simulated combustion gas of N2-10%CO-5%CO2-0.12%H 2S. An alternating stress profile was used with a minimum tensile stress of 0 MPa and a maximum tensile stress of 300 MPa (ten minute fatigue cycles). The results have demonstrated that the Gleeble can be used to successfully simulate the known corrosion fatigue cracking mechanism of Ni-based weld overlays in service. Multilayer corrosion scales developed on each of the claddings that consisted of inner and outer corrosion layers. The scales formed by the outward diffusion of cations and the inward diffusion of sulfur and oxygen anions. The corrosion fatigue behavior was influenced by the surface finish and the crack interactions. The initiation of a large number of corrosion fatigue cracks was not necessarily detrimental to the corrosion fatigue resistance. Finally, the as-received coextruded cladding exhibited the best corrosion fatigue resistance.

  8. The compensatory interaction between motor unit firing behavior and muscle force during fatigue.

    Science.gov (United States)

    Contessa, Paola; De Luca, Carlo J; Kline, Joshua C

    2016-10-01

    Throughout the literature, different observations of motor unit firing behavior during muscle fatigue have been reported and explained with varieties of conjectures. The disagreement amongst previous studies has resulted, in part, from the limited number of available motor units and from the misleading practice of grouping motor unit data across different subjects, contractions, and force levels. To establish a more clear understanding of motor unit control during fatigue, we investigated the firing behavior of motor units from the vastus lateralis muscle of individual subjects during a fatigue protocol of repeated voluntary constant force isometric contractions. Surface electromyographic decomposition technology provided the firings of 1,890 motor unit firing trains. These data revealed that to sustain the contraction force as the muscle fatigued, the following occurred: 1) motor unit firing rates increased; 2) new motor units were recruited; and 3) motor unit recruitment thresholds decreased. Although the degree of these adaptations was subject specific, the behavior was consistent in all subjects. When we compared our empirical observations with those obtained from simulation, we found that the fatigue-induced changes in motor unit firing behavior can be explained by increasing excitation to the motoneuron pool that compensates for the fatigue-induced decrease in muscle force twitch reported in empirical studies. Yet, the fundamental motor unit control scheme remains invariant throughout the development of fatigue. These findings indicate that the central nervous system regulates motor unit firing behavior by adjusting the operating point of the excitation to the motoneuron pool to sustain the contraction force as the muscle fatigues. Copyright © 2016 the American Physiological Society.

  9. Fatigue behavior and cumulative damage rule of concrete under cyclic compression with constant confined stress

    Institute of Scientific and Technical Information of China (English)

    ZHU Jin-song; GAO Chang-e; SONG Yu-pu

    2005-01-01

    The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm × 100mm × 100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen SN equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner's rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan's damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan' s damage formula are found to be in good agreement with the results of the experiments.

  10. Fatigue Behavior of Plain Concrete Under Biaxial Compression:Experiments and Theoretical Model

    Institute of Scientific and Technical Information of China (English)

    朱劲松; 宋玉普; 曹伟

    2003-01-01

    The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm×100 mm×100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predicted by this model is found to be in good agreement with the results of the experimental research.

  11. Notch fatigue behavior: Metallic glass versus ultra-high strength steel

    Science.gov (United States)

    Wang, X. D.; Qu, R. T.; Wu, S. J.; Duan, Q. Q.; Liu, Z. Q.; Zhu, Z. W.; Zhang, H. F.; Zhang, Z. F.

    2016-01-01

    Studying the effect of notch on the fatigue behavior of structural materials is of significance for the reliability and safety designing of engineering structural components. In this work, we conducted notch fatigue experiments of two high-strength materials, i.e. a Ti32.8Zr30.2Ni5.3Cu9Be22.7 metallic glass (MG) and a 00Ni18Co15Mo8Ti ultra-high strength steel (CM400 UHSS), and compared their notch fatigue behavior. Experimental results showed that although both the strength and plasticity of the MG were much lower than those of the UHSS, the fatigue endurance limit of the notched MG approached to that of the notched UHSS, and the fatigue ratio of the notched MG was even higher. This interesting finding can be attributed to the unique shear banding mechanism of MG. It was found that during fatigue process abundant shear bands formed ahead of the notch root and in the vicinity of the crack in the notched MG, while limited plastic deformation was observed in the notched UHSS. The present results may improve the understanding on the fatigue mechanisms of high-strength materials and offer new strategies for structural design and engineering application of MG components with geometrical discontinuities. PMID:27752136

  12. Fatigue Behavior of Friction Stir-Welded Joints Repaired by Grinding

    Science.gov (United States)

    Vidal, C.; Infante, V.

    2014-04-01

    Fatigue is undoubtedly the most important design criterion in aeronautic structures. Although friction stir-welded joints are characterized by a high mechanical performance, they can enclose some defects, especially in their root. These defects along with the relatively low residual stresses of the friction stir-welding thermomechanical cycle can turn into primary sources of crack initiation. In this context, this article deals with the fatigue behavior of friction stir-welded joints subjected to surface smoothing by grinding improvement technique. The 4-mm-thick aluminum alloy 2024-T351 was used in this study. The fatigue strength of the base material, joints in the as-welded condition, and the sound and defective friction stir-welded joints improved by grinding were investigated in detail. The tests were carried out with a constant amplitude loading and with a stress ratio of R = 0. The fatigue results show that an improvement in fatigue behavior was obtained in the joints repaired by superficial grinding technique. The weld grinding technique is better especially for lower loads and increases the high cycle fatigue strength. The fatigue strength of the improved welded joints was higher than that of the base material.

  13. Notch fatigue behavior: Metallic glass versus ultra-high strength steel

    Science.gov (United States)

    Wang, X. D.; Qu, R. T.; Wu, S. J.; Duan, Q. Q.; Liu, Z. Q.; Zhu, Z. W.; Zhang, H. F.; Zhang, Z. F.

    2016-10-01

    Studying the effect of notch on the fatigue behavior of structural materials is of significance for the reliability and safety designing of engineering structural components. In this work, we conducted notch fatigue experiments of two high-strength materials, i.e. a Ti32.8Zr30.2Ni5.3Cu9Be22.7 metallic glass (MG) and a 00Ni18Co15Mo8Ti ultra-high strength steel (CM400 UHSS), and compared their notch fatigue behavior. Experimental results showed that although both the strength and plasticity of the MG were much lower than those of the UHSS, the fatigue endurance limit of the notched MG approached to that of the notched UHSS, and the fatigue ratio of the notched MG was even higher. This interesting finding can be attributed to the unique shear banding mechanism of MG. It was found that during fatigue process abundant shear bands formed ahead of the notch root and in the vicinity of the crack in the notched MG, while limited plastic deformation was observed in the notched UHSS. The present results may improve the understanding on the fatigue mechanisms of high-strength materials and offer new strategies for structural design and engineering application of MG components with geometrical discontinuities.

  14. Fatigue behavior of press hardened Al-Si coated high strength steel

    Institute of Scientific and Technical Information of China (English)

    Wang Zijian; Gui Zhongxiang; Zhang Yisheng

    2014-01-01

    The fatigue behavior of press hardened Al-Si coated high strength steel has been investigated,and the fatigue strength turns out to be about 1 000 MPa. Surface morphology of fractured and non-fractured speci-men has been observed,and the coating shows significant influence on the fatigue behavior. The difference of elastic modulus between coating and substrate led to the main cracks perpendicular to the loading direction. The coating close to fracture exfoliated thinly,while the coating far away from the fracture kept integrated. Though the specimen was polished to obtain high surface quality,3 types of cracks occurred during the fatigue test. What’s more,inclusion particles were proved to play a crucial role in causing these cracks.

  15. STATIC AND FATIGUE BEHAVIOR OF IMPACTED AS4/PEEK THERMOPLASTIC COMPOSITES UNDER COMPRESSION LOAD

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Static and fatigue tests under compression load were made on impacted AS4/PEEK and T300/913C graphite/epoxy with [45/90/-45/0]5S stacking sequence. The comparison of the damage tolerance assessment for thermosetting and thermoplastic composites shows that thermoplastics are more damage tolerant under compression. Impacted thermoplastic composites have excellent compression-compression fatigue behavior. The damage growth life is only a few percent of their total fatigue life and no regular damage growth can be found. Some design principles for thermosetting composite structures may still be used.

  16. Fretting fatigue behavior of high-strength steel monostrands under bending load

    DEFF Research Database (Denmark)

    Winkler, Jan; Georgakis, Christos T.; Fischer, Gregor

    2015-01-01

    In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. To measure the local deformations on the strands, a novel method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires...... along the length of the monostrand. Information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of a monostrand undergoing flexural deformations is provided. From the series of dynamic fatigue tests, a fretting fatigue spectrum is derived...

  17. Thermo-mechanical response and fatigue behavior of shape memory alloy

    Energy Technology Data Exchange (ETDEWEB)

    Kusagawa, Masaki; Asada, Yasuhide; Nakamura, Toshiya [Tokyo Univ. (Japan). Dept. of Mechanical Engineering

    1998-11-01

    Mechanical, thermo-mechanical and fatigue behaviors of Ni-Ti-Nb shape memory alloy (SMA) have been studied to prepare material data for a design purpose. Presented are testing devices, testing procedure and test results of monotonic tensile, recovery of inelastic deformation due to post heating (thermo-mechanical recovery) and fatigue for future use of the SMA as a structural material of nuclear incore structures. (orig.)

  18. Effects of Contact Load on the Fretting Fatigue Behavior of IN-100 at Elevated Temperature

    Science.gov (United States)

    2009-03-01

    experimental setup which did not accurately model the turbine engine environment. Kawagoishi et al. [23] studied the nickel-based alloy Inconel 718 ...In their study with Inconel 718 [48, 49], it was found that the beneficial glaze oxide had formed and did affect the fretting fatigue life. Their...Waterhouse [52] investigated the fretting fatigue behaviors of austenitic steel type 321 and nickel-based alloy Inconel 718 at elevated temperatures. He

  19. Study on the Thermal Fatigue Behavior of Hot Deformed Wear Resistance Cast Iron and Effect of Carbide

    Institute of Scientific and Technical Information of China (English)

    Dong Litao; Liu Rongchang; Li Xingyuan; Chen Xiuhong

    2007-01-01

    The thermal fatigue behavior of wear resistance cast iron with different quantity of deformation has been investigated. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, approving that the more serious, the carbide breaks. The higher thermal fatigue resistance of wear resistance cast iron will be and thermal fatigue fracture belongs mainly to brittleness.

  20. High-temperature low cycle fatigue behavior of a gray cast iron

    Energy Technology Data Exchange (ETDEWEB)

    Fan, K.L., E-mail: 12klfan@tongji.edu.cn; He, G.Q.; She, M.; Liu, X.S.; Lu, Q.; Yang, Y.; Tian, D.D.; Shen, Y.

    2014-12-15

    The strain controlled low cycle fatigue properties of the studied gray cast iron for engine cylinder blocks were investigated. At the same total strain amplitude, the low cycle fatigue life of the studied material at 523 K was higher than that at 423 K. The fatigue behavior of the studied material was characterized as cyclic softening at any given total strain amplitude (0.12%–0.24%), which was attributed to fatigue crack initiation and propagation. Moreover, this material exhibited asymmetric hysteresis loops due to the presence of the graphite lamellas. Transmission electron microscopy analysis suggested that cyclic softening was also caused by the interactions of dislocations at 423 K, such as cell structure in ferrite, whereas cyclic softening was related to subgrain boundaries and dislocation climbing at 523 K. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain amplitudes. It showed that the higher the temperature, the rougher the crack face of the examined gray cast iron at the same total strain amplitude. Additionally, the microcracks were readily blunted during growth inside the pearlite matrix at 423 K, whereas the microcracks could easily pass through pearlite matrix along with deflection at 523 K. The results of fatigue experiments consistently showed that fatigue damage for the studied material at 423 K was lower than that at 523 K under any given total strain amplitude. - Highlights: • The low cycle fatigue behavior of the HT250 for engine cylinder blocks was investigated. • TEM investigations were conducted to explain the cyclic deformation response. • The low cycle fatigue cracks of HT250 GCI were studied by SEM. • The fatigue life of the examined material at 523 K is higher than that at 423 K.

  1. Fretting Fatigue Behavior of Shot-Peened IN 100

    Science.gov (United States)

    2006-03-01

    117 - x - List of Figures Figure Page Figure 1. Blade/ Disc ...Blade/ Disc Dovetail Joint in a Turbine Engine. - 7 - Figure 2. Simplified Fretting Configuration Contact Load (P) Fatigue Specimen (P...steam turbine power plants, medical applications, nuclear power systems, and in the chemical petrochemical industries 28. Nickel superalloys are

  2. Fatigue crack propagation behavior of ultrahigh molecular weight polyethylene.

    Science.gov (United States)

    Connelly, G M; Rimnac, C M; Wright, T M; Hertzberg, R W; Manson, J A

    1984-01-01

    The relative fatigue crack propagation resistance of plain and carbon fiber-reinforced ultrahigh molecular weight polyethylene (UHMWPE) was determined from cyclic loading tests performed on compact tension specimens machined from the tibial components of total knee prostheses. Both materials were characterized by dynamic mechanical spectroscopy, X-ray diffraction, and differential scanning calorimetry. The cyclic tests used loading in laboratory air at 5 Hz using a sinusoidal wave form. Dynamic mechanical spectroscopy showed that the reinforced UHMWPE had a higher elastic storage modulus than the plain UHMWPE, whereas X-ray diffraction and differential scanning calorimetry showed that the percent crystallinity and degree of order in the crystalline regions were similar for the two materials. Fatigue crack propagation in both materials proved to be very sensitive to small changes in the applied cyclic stress intensity range. A 10% increase in stress intensity resulted in approximately an order of magnitude increase in fatigue crack growth rate. The fatigue crack propagation resistance of the reinforced UHMWPE was found to be significantly worse than that of the plain UHMWPE. This result was attributed to poor bonding between the carbon fibers and the UHMWPE matrix and the ductile nature of the matrix itself.

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

    Science.gov (United States)

    Pollak, Randall D.

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

  4. Novel in situ device for investigating the tensile and fatigue behaviors of bulk materials

    Science.gov (United States)

    Ma, Zhichao; Zhao, Hongwei; Li, Qinchao; Wang, Kaiting; Zhou, Xiaoqin; Hu, Xiaoli; Cheng, Hongbing; Lu, Shuai

    2013-04-01

    For investigating the static tensile and dynamic fatigue behaviors of bulk materials, a miniaturized device with separate modular tensile and fatigue actuators was developed. The fatigue actuator presented good compatibility with the tensile actuator and mainly consisted of a special flexure hinge and piezoelectric stack. In situ fatigue tests under scanning electron microscope or metallographic microscope could be carried out due to the miniaturized dimensions of the device. A displacement correction method of tensile actuator based on load sensor compliance was investigated, and the feasibility of the method was verified by the comparison tests with a commercial tensile instrument. The application of testing the storage and loss modulus as a function of frequency was explained, and the temperature rises of both the piezoelectric stack and specimen were obtained as a function of frequency. Output characteristics of the fatigue actuator were also investigated. Additionally, the discharge performance of piezoelectric stack based on various initial voltages and fatigue tests on C11000 copper was carried out. This paper shows a modularized example that combines a servo motor with a piezoelectric actuator attached to the specimen grip to realize the in situ fatigue tests.

  5. Fatigue behavior of copper and selected copper alloys for high heat flux applications

    Energy Technology Data Exchange (ETDEWEB)

    Leedy, K.D.; Stubbins, J.F.; Singh, B.N.; Garner, F.A.

    1996-04-01

    The room temperature fatigue behavior of standard and subsize specimens was examined for five copper alloys: OFHC Cu, two CuNiBe alloys, a CuCrZr alloy, and a Cu-Al{sub 2}O{sub 3} alloy. Fatigue tests were run in strain control to failure. In addition to establishing failure lives, the stress amplitudes were monitored as a function of numbers of accrued cycles. The results indicate that the alloys with high initial yield strengths provide the best fatigue response over the range of failure lives examined in the present study: N{sub f} = 10{sup 3} to 10{sup 6}. In fact, the fatigue performance of the best alloys is dominated by the elastic portion of the strain range, as would be expected from the correlation of performance with yield properties. The alumina strengthened alloy and the two CuNiBe alloys show the best overall performance of the group examined here.

  6. Fatigue Behavior of High Speed Steel Roll Materials for Hot Rolling by Laser Impacting

    Institute of Scientific and Technical Information of China (English)

    ZHOU Li; SUN Da-le; LIU Chang-sheng; WU Qiong

    2006-01-01

    The fatigue behavior of high speed steel (HSS) roll materials for hot rolling was researched under water-cooling conditions by laser impacting. The microstructure of HSS sample and the morphologies of fatigue samples were observed by scanning electron microscope. The phase structure was detected by XRD. The morphology of situ oxide scale was observed by optical microscope, and the expansion coefficient was measured by TGA. The experiment results indicate that the cracks come into being at the carbide-matrix interface, but there are no cracks in the matrix after many times of laser impacting treatment, for the situ sample taken from the fractured roll surface, big carbides are more sensitive to the fatigue, and peel off prior to small ones. The relevant fatigue mechanisms are also discussed.

  7. Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, L. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, M. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-05-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

  8. Role of intermetallics on the mechanical fatigue behavior of Cu–Al ball bond interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Lassnig, A., E-mail: alice.lassnig@univie.ac.at [University of Vienna, Faculty of Physics, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien (Austria); Pelzer, R. [Infineon Technologies Austria AG, Siemensstrae 2, 9500 Villach (Austria); Gammer, C. [University of Vienna, Faculty of Physics, Physics of Nanostructured Materials, Boltzmanngasse 5, 1090 Wien (Austria); National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Khatibi, G. [Vienna University of Technology, Institute of Chemical Technology and Analytics, Getreidemarkt 9, 1060 Wien (Austria)

    2015-10-15

    The mechanical fatigue behavior of Cu–Al interfaces occurring in thermosonic ball bonds –typically used in microelectronic packages for automotive applications – is investigated by means of a specially designed fatigue test technique. Fully reversed cyclic shear stresses are induced at the bond interface, leading to subsequent fatigue lift off failure and revealing the weakest site of the bond. A special focus is set on the role of interfacial intermetallic compounds (IMC) on the fatigue performance of such interfaces. Therefore fatigue life curves were obtained for three representative microstructural states: The as-bonded state is compared to two annealed states at 200 °C for 200 h and at 200 °C for 2000 h respectively. In the moderately annealed state two IMC layers (Al{sub 2}Cu, Al{sub 4}Cu{sub 9}) could be identified, whereas in the highly aged state the original pad metallization was almost entirely consumed and AlCu is formed as a third IMC. Finally, the crack path is traced back as a function of interfacial microstructure by means of electron microscopy techniques. Whereas conventional static shear tests reveal no significant decrease of the bond shear force with increased IMC formation the fatigue tests prove a clear degradation in the cyclic mechanical performance. It can be concluded that during cycling the crack deflects easily into the formed intermetallics, leading to early failure of the ball bonds due to their brittle nature. - Highlights: • High cycle fatigue of various miniaturized Cu–Al interfaces is investigated. • Interfacial intermetallic compounds consist of Al2Cu, AlCu and Al4Cu9. • Static shear strength shows minor dependency on interfacial phase formation. • Fatigue tests prove significant degradation with intermetallic compound evolution. • Fatigue fracture surface analysis reveal microstructure dependent crack path.

  9. Influence of microstructural purity on the bending fatigue behavior of VAR-melted superelastic Nitinol.

    Science.gov (United States)

    Launey, Maximilien; Robertson, Scott W; Vien, Lot; Senthilnathan, Karthikeyan; Chintapalli, Prashanth; Pelton, Alan R

    2014-06-01

    The bending fatigue resistance of commercially-available Standard versus High Purity Nitinol was evaluated at 3% mean strain and a range of strain amplitudes with the simple wire Z-specimen geometry. The Standard grade Nitinol demonstrated a 10(7)-cycle fatigue strain limit of 0.50% alternating strain, comparable to results reported elsewhere in the literature. Conversely, the High Purity grade VAR Nitinol demonstrated a 5-fold improvement in fatigue resistance with an impressive 10(7)-cycle fatigue strain limit of 2.5% alternating strain. The High Purity Nitinol has an oxygen+nitrogen content of 60wppm, maximum wrought-material inclusion length of 17µm, and inclusion volume fraction of 0.28%, all substantially less than industry standards. With all processing variables held constant except for inclusion content, it is clear that this marked fatigue superiority is due exclusively to the reduction in both size and area fraction of inclusions. Copyright © 2014 Elsevier Ltd. All rights reserved.

  10. Effect of strain rate and temperature at high strains on fatigue behavior of SAP alloys

    DEFF Research Database (Denmark)

    Blucher, J.T.; Knudsen, Per; Grant, N.J.

    1968-01-01

    Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased with decre......Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased...

  11. Influence of Grain Boundary on Fatigue Behavior of Ni-base Bicrystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The influence of the grain boundary on the fatigue behavior was studied by two three-point-bending (TPB) specimens.One TPB specimen was named Bicrystal 1, whose pre-crack was along the grain boundary and the applied loadparalleled to pre-crack direction, while the other TPB specimen was named Bicrystal 2, whose the pre-crack wasperpendicular to the grain boundary and the applied load paralleled also to the pre-crack. It was found that the rateof the fatigue crack growth of Bicrystal 1 was about a tenfold higher than that of Bicrystal 2. The fatigue behaviorof Bicrystal 2 specimens was dependent on the distance between the crack tip and grain boundary. The crack growthrate was highest when the crack tip was at a critical distance to the grain boundary, while the rate was the lowestwhen the crack tip reached grain boundary. After the crack was over the grain boundary, the crack growth rateincreased. The crystallographic finite element method was applied to analyze the stress and strain structure aheadof the crack, in order to reveal the above characteristics of the fatigue behavior. It is the grain boundary-inducedredistribution of stresses near the crack tip that induces the difference of fatigue behavior.

  12. Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part II: Fatigue Life and Fracture Behavior

    Science.gov (United States)

    Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

    2014-10-01

    Influence of nitrogen content on low cycle fatigue life and fracture behavior of 316LN stainless steel (SS) alloyed with 0.07 to 0.22 wt pct nitrogen is presented in this paper over a range of total strain amplitudes ( ±0.25 to 1.0 pct) in the temperature range from 773 K to 873 K (500 °C to 600 °C). The combined effect of nitrogen and strain amplitude on fatigue life is observed to be complex i.e., fatigue life either decreases/increases with increase in nitrogen content or saturates/peaks at 0.14 wt pct N depending on strain amplitude and temperature. Coffin-Manson plots (CMPs) revealed both single-slope and dual-slope strain-life curves depending on the test temperature and nitrogen content. 316LN SS containing 0.07 and 0.22 wt pct N showed nearly single-slope CMP at all test temperatures, while 316LN SS with 0.11 and 0.14 wt pct N exhibited marked dual-slope behavior at 773 K (500 °C) that changes to single-slope behavior at 873 K (600 °C). The changes in slope of CMP are found to be in good correlation with deformation substructural changes.

  13. Fatigue Behavior of HDPE Composite Reinforced with Silane Modified TiO_2

    Institute of Scientific and Technical Information of China (English)

    C.X. Dong; S.J. Zhu; Mineo Mizuno; Masami Hashimoto

    2011-01-01

    The composite of high density polyethylene reinforced with silane-modified TiO2 particles (silane-TiO2/HDPE) is a potential bone substitute biomaterial. The structure, bioactivity, and mechanical properties of silane-TiO2/HDPE are analogous to those of natural bone, correspondingly. In order to investigate the effect of silane connection and saline solution on fatigue behaviors, flexural fatigue tests with this composite were carried out in both air and saline solution. Saline solution was found to have different effect on fatigue life. In saline solution, the fatigue life could be improved at stress levels lower than 30 MPa, while the fatigue life could be reduced at stress levels higher than 30 MPa. After analyzing the fracture morphologies, different failure mechanisms were proposed, and the important role of silane connection in the composite during the fatigue process was discussed. Silane connection cannot only support the loading stress but also hinder the failure process under loading effectively. For dry specimens, no interfacial failure between the filler and matrix was found. For wet specimens, it is inferred that the synergetic effect of saline solution and high concentrated stress at high stress level could easily destroy the silane connection, which accelerated the fracture process, whereas the synergetic effect of saline solution and silane connection at low stress level could promote the formation of more microcracks on sample surface, which hindered the final fracture.

  14. Low cycle fatigue behavior in a medium-carbon carbide-free bainitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Kang, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, F.C., E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Long, X.Y. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, B. [College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2016-06-01

    In the paper, different morphologies of bainite were obtained through isothermal quenching at 320 °C and 395 °C in a medium-carbon carbide-free bainitic steel. The cyclic deformation mechanism was explored by using low cycle fatigue testing. The volume fraction of retained austenite was measured by X-ray diffraction and the space partitioning of the solute atoms was constructed by three-dimensional atom probe. Results showed that the fatigue life at 320 °C was always higher than that at 395 °C under low and high total strain amplitude. The cyclic softening at the early fatigue stage increased the plastic strain of the sample which was responsible for the reduction of the fatigue life at 395 °C. Strain-induced retained austenite to martensite contributed to initial cyclic hardening, but almost having no effect on the subsequent cyclic stable/softening behaviors. The finer bainitic ferrite sheaves obtained at 320 °C changed the small fatigue crack propagation direction and delayed the crack propagation rate, which was beneficial for the fatigue properties. In addition, the substitutional atoms did not redistribute between the retained austenite and bainitic ferrite before and after cyclic deformation.

  15. Creep-fatigue behavior of turbine disc of superalloy GH720Li at 650 °C and probabilistic creep-fatigue modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Dianyin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China); Ma, Qihang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Shang, Lihong [Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5 (Canada); Gao, Ye [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Wang, Rongqiao, E-mail: wangrq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China)

    2016-07-18

    Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li at an elevated temperature of 650 °C with a stress ratio of 0.1, based on which, different dwell times at the maximum loading were applied to investigate the effect of dwell time on the creep-fatigue behaviors. The tested specimens were cut from the rim region of an actual turbine disc in the hoop direction. The grain size and precipitates of the GH720Li superalloy were examined through scanning electronic microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Experimental data shows creep-fatigue lifetime decreases as the dwell time prolongs. Further, different scattering was observed in the creep-fatigue lifetime at different dwell times. Then a probabilistic model based on the applied mechanical work density (AMWD), with a linear heteroscedastic function that evaluates the non-constant deviation in the creep-fatigue lifetime, was formulated to describe the dependence of creep-fatigue lifetime on the dwell time. Finally, the possible microscopic mechanism of the creep-fatigue behavior has been discussed by SEM with EDS on the fracture surfaces.

  16. Fatigue Behavior of Ultrafine-Grained 5052 Al Alloy Processed Through Different Rolling Methods

    Science.gov (United States)

    Yogesha, K. K.; Joshi, Amit; Jayaganthan, R.

    2017-05-01

    In the present study, 5052 Al alloy was processed through different rolling methods to obtain ultrafine grains and its high-cycle fatigue behavior were investigated. The solution-treated Al-Mg alloys (AA 5052) were deformed through different methods such as cryorolling (CR), cryo groove rolling (CGR) and cryo groove rolling followed by warm rolling (CGW), up to 75% thickness reduction. The deformed samples were subjected to mechanical testing such as hardness, tensile and high-cycle fatigue (HCF) test at stress control mode. The CGW samples exhibit better HCF strength when compared to other conditions. The microstructure of the tested samples was characterized by optical microscopy, SEM fractography and TEM to understand the deformation behavior of deformed Al alloy. The improvement in fatigue life of CR and CGR samples is due to effective grain refinement, subgrain formations, and high dislocation density observed in the heavily deformed samples at cryogenic condition as observed from SEM and TEM analysis. However, in case of CGW samples, formation of nanoshear bands accommodates the applied strain during cyclic loading, thereby facilitating dislocation accumulation along with subgrain formations, leading to the high fatigue life. The deformed or broken impurity phase particles found in the deformed samples along with the precipitates that were formed during warm rolling also play a prominent role in enhancing the fatigue strength. These tiny particles hindered the dislocation movement by effectively pinning it at grain boundaries, thereby improving the resistance of crack propagation under cyclic load.

  17. Effects of microstructure on fatigue crack growth behavior in cold-rolled dual phase steels

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shengci [School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kang, Yonglin, E-mail: kangylin@ustb.edu.cn [School of Materials Science and Engineering, State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Kuang, Shuang [Technical Research Institute, Shougang Corporation, Ltd., Beijing 100043 (China)

    2014-08-26

    Fatigue crack growth behaviors of cold-rolled dual phase steels with different microstructures were investigated at room temperature. The ferrite–martensite dual-phase microstructure was obtained by intercritical annealing. Fatigue crack growth (FCG) behaviors were described by both the Paris model and a new exponential model; fatigue fractography and surface morphology near the fracture were arrested by scanning electron microscopy (SEM); the relationship between macroscopic and microcosmic FCG rate was analyzed quantificationally. The results showed that both the models can be used to describe the fatigue crack growth rate of the samples rather well; fatigue striations and secondary cracks were observed in the fracture surface at stable expanding region (II), while the fracture at rapid expanding region (III) combined dimple and quasi-cleavage morphology; the roughness of fracture surface and the degree of secondary cracking increased with an increase in martensite content, leading to a higher threshold value. Moreover, the changes of microcosmic FCG rate were smoother than that of the macroscopic FCG rate.

  18. Low Cycle Fatigue Behaviors of Alloy 617 (INCONEL 617 Weldments for High Temperature Applications

    Directory of Open Access Journals (Sweden)

    Rando Tungga Dewa

    2016-04-01

    Full Text Available In this study, we comparatively investigate the low cycle fatigue behavior of Alloy 617 (INCONEL 617 weldments by gas tungsten arc welding process at room temperature and 800 °C in the air to support the qualification in high temperature applications of the Next Generation-IV Nuclear Plant. Axial total-strain controlled tests have been performed with the magnitude of strain ranges with a constant strain ratio (Rε = −1. The results of fatigue tests consistently show lower fatigue life with an increase in total strain range and temperature at all testing conditions. The reduction in fatigue life may result from the higher cyclic plastic strain accumulation and the material ductility at high temperature conditions. A constitutive behavior of high temperature by some cyclic hardening was observed. The occurrence of serrated yielding in the cyclic stress response was also observed, suggesting the influence of dynamic strain aging during high temperature. We evaluated a well-known life prediction model through the Coffin-Manson relationship. The results are well matched with the experimental data. In addition, low cycle fatigue cracking occurred in the weld metal region and initiated transgranularly at the free surface.

  19. Mechanical Properties and Fatigue Behavior of Unitized Composite Airframe Structures at Elevated Temperature

    Science.gov (United States)

    2016-09-01

    suitability of this composite for use in aerospace components designed to contain high-temperature environments, mechanical tests were performed under... contain high-temperature environments, mechanical tests were performed under temperature conditions simulating the actual operating conditions. In all... MECHANICAL PROPERTIES AND FATIGUE BEHAVIOR OF UNITIZED COMPOSITE AIRFRAME STRUCTURES AT ELEVATED

  20. Childhood maltreatment and the response to cognitive behavior therapy for chronic fatigue syndrome.

    NARCIS (Netherlands)

    Heins, M.J.; Knoop, H.; Lobbestael, J.; Bleijenberg, G.

    2011-01-01

    Objective: To examine the relationship between a history of childhood maltreatment and the treatment response to cognitive behavior therapy for chronic fatigue syndrome (CFS). Methods: A cohort study in a tertiary care clinic with a referred sample of 216 adult patients meeting the Centers for Disea

  1. [Both aerobic exercise and cognitive-behavioral therapy reduce fatigue in FSHD: an RCT

    NARCIS (Netherlands)

    Voet, V.B.M.; Bleijenberg, G.; Hendriks, J.C.M.; Groot, I.J.M. de; Padberg, G.W.; Engelen, B.G.M. van; Geurts, A.C.H.

    2015-01-01

    OBJECTIVE: To investigate the effect of aerobic exercise training (AET) and cognitive-behavioral therapy (CBT) on chronic fatigue in patients with facioscapulohumeral muscular dystrophy (FSHD). DESIGN: A multicenter, assessor-blinded, randomized clinical trial (Dutch Trial Register No 1447). METHOD:

  2. Both aerobic exercise and cognitive-behavioral therapy reduce chronic fatigue in FSHD: An RCT

    NARCIS (Netherlands)

    Voet, N.B.; Bleijenberg, G.; Hendriks, J.C.M.; Groot, I.M. de; Padberg, G.W.; Engelen, B.G. van; Geurts, A.C.

    2014-01-01

    OBJECTIVE: To investigate the effect of aerobic exercise training (AET) and cognitive-behavioral therapy (CBT) on chronic fatigue in patients with facioscapulohumeral muscular dystrophy (FSHD). METHODS: We performed a multicenter, assessor-blinded, randomized clinical trial (RCT). Fifty-seven patien

  3. Childhood maltreatment and the response to cognitive behavior therapy for chronic fatigue syndrome.

    NARCIS (Netherlands)

    Heins, M.J.; Knoop, H.; Lobbestael, J.; Bleijenberg, G.

    2011-01-01

    Objective: To examine the relationship between a history of childhood maltreatment and the treatment response to cognitive behavior therapy for chronic fatigue syndrome (CFS). Methods: A cohort study in a tertiary care clinic with a referred sample of 216 adult patients meeting the Centers for

  4. Childhood maltreatment and the response to cognitive behavior therapy for chronic fatigue syndrome

    NARCIS (Netherlands)

    Heins, M.J.; Knoop, H.; Lobbestael, J.; Bleijenberg, G.

    2011-01-01

    OBJECTIVE: To examine the relationship between a history of childhood maltreatment and the treatment response to cognitive behavior therapy for chronic fatigue syndrome (CFS). METHODS: A cohort study in a tertiary care clinic with a referred sample of 216 adult patients meeting the Centers for

  5. Bond and low cycle fatigue behavior of thermoset composite reinforcing for the concrete industry

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, B.

    1990-09-21

    This thesis encompasses two separate research projects. The first project, described in Chapter 2 was a project investigating the fatigue behavior of thermoset Fiber Composite (FC) sandwich wall ties. The second research project detailed in this thesis was a project studying the bond and tensile properties of FC rod and FC fibers.

  6. Effect of strain rate and temperature at high strains on fatigue behavior of SAP alloys

    DEFF Research Database (Denmark)

    Blucher, J.T.; Knudsen, Per; Grant, N.J.

    1968-01-01

    Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased...

  7. Implementing Cognitive Behavioral Therapy for Chronic Fatigue Syndrome in a Mental Health Center: A Benchmarking Evaluation

    Science.gov (United States)

    Scheeres, Korine; Wensing, Michel; Knoop, Hans; Bleijenberg, Gijs

    2008-01-01

    Objective: This study evaluated the success of implementing cognitive behavioral therapy (CBT) for chronic fatigue syndrome (CFS) in a representative clinical practice setting and compared the patient outcomes with those of previously published randomized controlled trials (RCTs) of CBT for CFS. Method: The implementation interventions were the…

  8. The impact of informational interventions about cognitive behavioral therapy for chronic fatigue syndrome on GPs referral behavior.

    NARCIS (Netherlands)

    Scheeres, K.; Wensing, M.J.P.; Mes, C.; Bleijenberg, G.

    2007-01-01

    OBJECTIVE: This study investigated the impact of an informational intervention among general practitioners (GPs) about a new treatment with cognitive behavioral therapy (CBT) for chronic fatigue syndrome (CFS) in a mental health center (MHC). The outcome measures concerned GPs knowledge and attitude

  9. The cyclic fatigue behavior of a Nicalon/SiC composite

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J. [Univ. of Tennessee, Knoxville, TN (United States); Snead, L.L. [Oak Ridge National Lab., TN (United States)

    1996-10-01

    Cyclic fatigue tests were performed at ambient temperature on a Nicalon/SiC composite to study the effects of fabric orientation on the mechanical behavior. Four-point bend specimens were loaded either parallel or normal to the braided fabric plies. The maximum stresses chosen during the fatigue tests were 60, 70, and 80% of the monotonic strengths, respectively, in both orientations. Specimen failure did not occur in any case even after one million loading cycles. However, it was observed that much of the decrease in the composite modulus occurred in the first few (<10) cycles, and the fabric orientation did not significantly affect the effective modulus or midspan deflection trends.

  10. Experimental evaluation of the fretting fatigue behavior of high-strength steel monostrands

    DEFF Research Database (Denmark)

    Winkler, Jan; Fischer, Gregor; Georgakis, Christos T.

    2013-01-01

    . Moreover, the paper provides relevant information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of the monostrand undergoing flexural deformations. The results presented herein are of special interest for the fatigue analysis of modern stay......In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. A method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires along the length of the monostrand. The experimental data...

  11. Long Term Fatigue Behavior of Zirconia Based Dental Ceramics

    Directory of Open Access Journals (Sweden)

    Moustafa N. Aboushelib

    2010-04-01

    Full Text Available This study evaluated the influence of cyclic loading on zirconia bar-shaped specimens after being subjected to three different surface treatments: particle abrasion with either 50 μm or 110 μm alumina and grinding with diamond points, while polished specimens served as a control. Statistical analysis revealed significant reduction (38-67% in flexure strength (P < 0.001 after three million cycles of dynamic loading for all surface treatments. Scanning electron imaging revealed grain boundary thickening, grain pull-out, and micro-cracking as the main structural defects. The results suggest that various surface treatments of zirconia based dental ceramics may significantly influence their long term fatigue resistance in the oral environment.

  12. Impact and residual fatigue behavior of ARALL and AS6/5245 composite material

    Science.gov (United States)

    Johnson, W. S.

    1989-01-01

    The impact sensitivity of aramide fiber-reinforced aluminum laminates (ARALL) was investigated by testing two types of ARALL (7075 aluminum prestrained and 2024 aluminum not prestrained), via static indentation, and the results were compared to those of sheet aluminum alloys 7075-T6 and 2024-T3 and to a state of the art composite AS6/5245. It was found that the impact resistance of the two ARALL samples was inferior to that of monolithic sheet aluminum samples, although the ARALL material made with 2024-T3 aluminum was superior to that made with 7075-T6 aluminum. The impact damage resistance of ARALL materials was at least equal to that of AS6/5245, and the AS6/5245 had higher residual tension-tension fatigue strength after impact than the ARALL samples. It was also found that the prestraining of the ARALL reduced the fatigue growth of impact damage.

  13. Fatigue behavior of asphalt mixtures colombian with addition recycled pavement asphalt to 100 %

    Directory of Open Access Journals (Sweden)

    Neidy Betssey Patiño Boyacá

    2015-01-01

    Full Text Available This research was conducted in order to establish the fatigue behavior of asphalt mixtures with gradations MD20 Instituto de Desarrollo Urbano (IDU and MDC 2 of The Instituto Nacional de Vías (INVIAS, with addition of recycled granular flexible pavement (RAP with asphalt of penetration 60/70 and 80/100. The first step was to characterize the asphalt and RAP as well as calculate the optimum percentage of asphalt to be added to 100 % RAP mixtures. Then samples were fabricated with different trapezoidal gradations and asphalt, to be tested finally fatigue at different deformations. Among the results found, it was determined that the tested mixtures have a high stiffness; although, it varies depending on the asphalt mix used and that the best fatigue life with respect to those studied is the MDC-2 with bitumen 80/100.

  14. Low cycle fatigue behaviors of elbow pipe with local wall thinning

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Koji, E-mail: ktaka@ynu.ac.j [Faculty of Engineering, Yokohama National University, 79-5, Tokiwadai, Hodogaya, Yokohama, 240-8501 (Japan); Watanabe, Sota; Ando, Kotoji [Faculty of Engineering, Yokohama National University, 79-5, Tokiwadai, Hodogaya, Yokohama, 240-8501 (Japan); Urabe, Yoshio [Japan Nuclear Technology Institute, 7F Shiba Bldg., 4-2-3, Shiba, Minato-ku, Tokyo, 108-0014 (Japan); Hidaka, Akitaka; Hisatsune, Masakazu [Hitachi-GE Nuclear Energy, Ltd., 3-1-1, Saiwai-cho, Hitachi, Ibaraki, 317-8511 (Japan); Miyazaki, Katsumasa [Hitachi, Ltd., 3-1-1, Saiwai-cho, Hitachi, Ibaraki, 317-8511 (Japan)

    2009-12-15

    Low cycle fatigue tests were conducted using 100A elbow specimens made of STPT410 carbon steel with local wall thinning. Local wall thinning by erosion/corrosion was simulated by machined pipe wall thinning. The local wall thinning areas were located at three different areas, called extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. The effects of eroded conditions, such as eroded ratio, eroded angle and position, on the low cycle fatigue behavior and fatigue life were discussed by using experimental results and finite element analyses. Also the location of crack initiation and the crack growth direction could be predicted by three dimensional elasto-plastic finite element analyses. In addition, the safety margin of eroded elbows against seismic loading was discussed by comparing the fictitious stress of elbows with the allowable stress limit demanded by the design code.

  15. Fatigue behavior of a thermally-activated NiTiNb SMA-FRP patch

    Science.gov (United States)

    El-Tahan, M.; Dawood, M.

    2016-01-01

    This paper presents the details of an experimental study that was conducted to characterize the fatigue behavior of a thermally-activated shape memory alloy (SMA)/carbon fiber reinforced polymer (CFRP) patch that can be used to repair cracked steel members. A total of 14 thermally-activated patches were fabricated and tested to evaluate the stability of the prestress under fatigue loading. The parameters considered in this study are the prestress level in the nickel-titanium-niobium SMA wires and the applied force range. An empirical model to predict the degradation of the prestress is also presented. The results indicate that patches for which the maximum applied loads in a fatigue cycle did not cause debonding of the SMA wires from the CFRP sustained two million loading cycles with less than 20% degradation of the prestress.

  16. Fatigue Behavior of 2A12 Aluminum Alloy Under Multiaxial Loading

    Directory of Open Access Journals (Sweden)

    CHEN Ya-jun

    2017-08-01

    Full Text Available The multiaxial fatigue behavior of 2A12 aluminum alloy was studied with SDN100/1000 electro-hydraulic servo tension-torsion fatigue tester under multiple variables, and the failure mechanism was investigated by scanning electron microscopy (SEM. The results show that under the loading condition of equivalent stress, the fatigue life decreases with the increase of phase angle. For the phase angle 0°, some special features can be observed in the crack initial zone, such as the tire pattern,fishbone pattern and stalactite pattern. There are secondary cracks and vague fatigue striations in the crack propagation zone; the multiaxial fatigue life decreases with the change of mean stress for tension or torsion. Some white flocculent oxides can be found in the crack initiation zone, and secondary crack as well as shear-type elongated dimples in the instantaneous fracture zone; facing different loading waveforms, the multiaxial life of sine wave is the longest, triangle wave in the second place, and the square wave is the shortest, under the loading condition of equivalent stress, square wave leads to the maximum structural energy dissipation. Under the low and high two step loading, 2A12 shows training effect.

  17. The low cycle fatigue behavior of a plasma-sprayed coating material

    Science.gov (United States)

    Gayda, J.; Gabb, T. P.; Miner, R. V., Jr.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  18. FATIGUE ASSOCIATED EMG BEHAVIOR OF THE FIRST DORSAL INTEROSSEOUS AND ADDUCTOR POLLICIS MUSCLES IN DIFFERENT GROUPS OF SUBJECTS

    NARCIS (Netherlands)

    ZIJDEWIND, Inge; KERNELL, D

    1994-01-01

    We have studied the fatigue-associated behavior of surface EMG in two histochemically different muscles of the hand: fi rst dorsal interosseous (FDI) and adductor pollicis (AP; relatively more type I fibers in AP than in FDI). During a fatigue test evoked by electrical stimulation of the ulnar nerve

  19. The Effects of Cognitive Behavioral Therapy for Postcancer Fatigue on Perceived Cognitive Disabilities and Neuropsychological Test Performance

    NARCIS (Netherlands)

    Goedendorp, Martine M.; Knoop, Hans; Gielissen, Marieke F. M.; Verhagen, Constans A. H. H. V. M.; Bleijenberg, Gijs

    2014-01-01

    Context. After successful cancer treatment, a substantial number of survivors continue to experience fatigue and related concentration and memory problems. Severe fatigue after cancer treatment can be treated effectively with cognitive behavioral therapy (CBT), but it is unclear whether CBT has an e

  20. Subtask 12D6: Fatigue behavior of unirradiated V-5Cr-5Ti

    Energy Technology Data Exchange (ETDEWEB)

    Gieseke, B.G.; Stevens, C.O.; Grossbeck, M.L. [Oak Ridge National Lab., TN (United States)

    1995-03-01

    The objective of this research is to determine the low cycle fatigue behavior of V-5Cr-5Ti alloys for a range of temperatures and the extent of environmental effects at ambient temperatures. The results of in-vacuum low cycle fatigue tests are presented for unirradiated V-5Cr-5Ti tested at room temperature (25, 250, and 400{degrees}C). A comparison of the fatigue data generated in rough and high vacuums shows that a pronounced environmental degradation of the fatigue properties exists in the alloy at room temperature. Fatigue life was reduced by as much as 84%. Cyclic stress range data and SEM observations suggest that this reduction is due to a combination of increases in rates of crack initiation and subsequent growth. The relative contribution of each difference is dependent upon the strain range. In high vacuum, the fatigue results also show a trend of increasing cyclic life with increasing temperature between 25 and 400{degrees}C. From the limited data available, life at 25{degrees}C averages 1.7 times that at 25{degrees}C, and at 400{degrees}C, life averages 3.2 times that at room temperature. Like the environmental effects at 25{degrees}C, the effect of temperature seems to be a function of strain range at each temperature. The total strain range and cycles to failure were correlated using a power law relationship and compared to 20% cold-worked 316 stainless steel and several vanadium-base alloys. The results suggest that V-SCr-5Ti has better resistance to fatigue than 316-SS in the temperature range of 25 to 400{degrees}C. At 400{degrees}C, the data also show that V-5Cr-5Ti out performs Vanstar alloys 7 and 8 over the entire range of strains investigated. Furthermore, the fatigue properties of the V-5Cr-5Ti alloy compare favorably to V-15Cr-57i (at 25{degrees}C) and Vanstar 9 (at 400{degrees}C) at strains greater than 1%. At lower strains, the lower fatigue resistance of V-5Cr-5Ti is attributed to the higher strengths of the V-15Cr-5Ti and Vanstar 9 alloys.

  1. Corrosion fatigue behavior of fastening hole structure and virtual crack propagation tests

    Institute of Scientific and Technical Information of China (English)

    Youhong Zhang; Xinlong Chang; Guozhi Lv; Hui Wang; Zhong Li; Yueliang Cheng

    2008-01-01

    The fatigue crack propagation behavior of the LY12CZ aluminum alloy fastener involving a central hole in air or in 3.5wt% NaC1 solution was investigated. The experimental results indicated that the corrosion fatigue crack growth rate decreased with the increasing loading frequency, and in a corrosive environment, the crack growth rate was slightly larger than that in air.Based on the experimental results, the virtual corrosion fatigue crack propagation tests were investigated and the stochastic process method and the AFGROW simulation method were presented. The normal process and lognormal process were considered for the stochastic process method based on the numerically fitted Paris equation. The distribution of crack size and the corresponding prob-abilistic model of crack length distribution for a given number of cycles can be found by integrating the stochastic process over time.Using the AFGROW software, the virtual simulation was carried out to analyze the corrosion fatigue crack growth behavior and the predicted crack growth curve was in good agreement with the experimental results.

  2. Ti–6Al–4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China); Li, Shaolin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Qi, Hongyu, E-mail: qhy@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China)

    2014-03-01

    The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti–6Al–4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone.

  3. Phase Transformation Behavior and Resistance to Bending and Cyclic Fatigue of ProTaper Gold and ProTaper Universal Instruments.

    Science.gov (United States)

    Hieawy, Ahmed; Haapasalo, Markus; Zhou, Huimin; Wang, Zhe-Jun; Shen, Ya

    2015-07-01

    The purpose of this study was to compare the flexibility and cyclic fatigue resistance of ProTaper Universal (PTU; Dentsply Tulsa Dental Specialities, Tulsa, OK) and ProTaper Gold (PTG; Dentsply Tulsa Dental Specialities, Tulsa, OK) instruments in relation to their phase transformation behavior. Sizes S1, S2, F1, F2, and F3 of PTU and PTG instruments were subjected to rotational bending at a curvature of 40° and a radius of 6 mm. The number of cycles to fracture (NCF) was recorded. The fracture surface of all fragments was examined with a scanning electron microscope. Flexibility was determined by 45° bending tests according to the ISO 3630-1 specification. Unused and fractured instruments were examined by differential scanning calorimetry. PTG had a cyclic fatigue resistance superior to PTU in all sizes (P difference in the NCF of PTU instruments was detected between F1 and F2. The fractured files of both PTU and PTG showed the typical fracture pattern of fatigue failure. The bending load values were significantly lower for PTG than for PTU (P difference in the austenite finish between unused files and instruments subjected to the fatigue process. PTG files were significantly more flexible and resistant to fatigue than PTU files. PTG exhibited different phase transformation behavior than PTU, which may be attributed to the special heat treatment history of PTG instruments. PTG may be more suited for preparing canals with a more abrupt curvature. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  4. SEM in-situ investigation on fatigue cracking behavior of P/M Rene95 alloy with surface inclusions

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The low-cycle fatigue behavior of powder metallurgy Rene95 alloy containing surface inclusions was investigated by in-situ observation with scanning electron microscopy (SEM). The process of fatigue crack initiation and early stage of propagation behavior indicates that fatigue crack mainly occurs at the interface between the inclusion and the matrix. The effect of inclusion on the fatigue crack initiation and the early stage of crack growth was very obvious. The fatigue crack growth path in the matrix is similar to the shape of inclusion made on the basis of fatigue fracture image analysis. The empiric relation between the surface and inside crack growth length, near a surface inclusion, can be expressed. Therefore, the fatigue crack growth rate or life of P/M Rene95 alloy including the inclusions can be evaluated on the basis of the measurable surface crack length parameter. In addition, the effect of two inclusions on the fatigue crack initiation behavior was investigated by the in-situ observation with SEM.

  5. The monitoring and fatigue behavior of CFCCs at ambient temperature and 1000{degrees}C

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; McHargue, C.J. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1997-04-01

    Metallographically polished flexure bars of Nicalon/SiC and Nicalon/alumina composites were subjected to monotonic and cycle-fatigue loadings, with loading either parallel or normal to the fabric plies. The fabric orientation did not significantly affect the mechanical behavior of the Nicalon/SiC composite at ambient temperature. However, the mechanical behavior of the Nicalon/alumina composite was significantly affected by the fabric orientation at ambient temperature in air and at 1000{degrees}C in argon atmosphere. In addition, there was a significant degradation in the fatigue performance of the alumina matrix composite at the elevated temperature, owing to creep in the material and degradation in the fiber strength.

  6. Fatigue crack behavior on a Cu-Zn-Al SMA

    Directory of Open Access Journals (Sweden)

    V. Di Cocco

    2014-10-01

    Optical Microscope (LOM observations. Furthermore a fatigue crack propagation and fracture surface scanning electron microscope (SEM observations have been performed in order to evaluate the crack path and the main crack micromechanisms.

  7. Effects of voids on delamination behavior under static and fatigue mode I and mode II

    Science.gov (United States)

    Abdelal, Nisrin Rizek

    Composite materials have become materials of choice for wind turbine blade manufacturing due to their high specific stiffness, strength and fatigue life. Glass fiber composites are used extensively in light-weight structural components for wind turbines, aircrafts, marine craft and high performance automobile because glass fiber is inexpensive and usually provides high strength to weight ratio and good in-plane mechanical properties. The high cycle fatigue resistance of composite materials used in wind turbine blades has been recognized as a major uncertainty in predicting the reliability of wind turbines over their design lifetime. Blades are expected to experience 108 to 109 fatigue cycles over a 20 to 30 year lifetime. Delamination or interlaminar failure is a serious failure mode observed in composite structures. Even partial delamination will lead to a loss of local stiffness, which can preclude buckling failure. Manufacturing process defects such as voids and fiber waviness degrade the fatigue life and delamination resistance of the blade's composite. This research describes the effect of voids on static and fatigue interlaminar fracture behavior under mode I and mode II loading of wind turbine glass fiber composites. Samples with different void volume fractions in the 0.5%-7% range were successfully obtained by varying the vacuum in the hand layup vacuum bagging manufacturing process. Void content was characterized using four different methods; ultrasonic scanning, epoxy burn off, serial sectioning and X-Ray computed tomography. The effect of voids on both mode I and mode II interlaminar fracture toughness under static and fatigue loading was investigated. Finally, fractographic analysis (using optical and scanning electron microscopy) was conducted. The results showed that voids leads to slight reduction in static modes I and II interlaminar fracture toughness. In addition, voids lead to a decrease in modes I and II maximum cyclic strain energy release

  8. Fatigue and Fracture Behavior of a Cold-Drawn Commercially Pure Aluminum Wire

    Directory of Open Access Journals (Sweden)

    Jia-Peng Hou

    2016-09-01

    Full Text Available Fatigue properties and cracking behavior of cold-drawn commercially pure aluminum wires (CPAWs widely used as the overhead transmission conductors were investigated. It was found that the fracture surface of the CPAWs shows an obvious four-stage fracture characteristic, i.e., crack initiation, planar crack propagation, 45°-inclined crack propagation and final rapid fracture. The crack growth mechanisms for the CPAWs were found quite different from those for the conventional coarse-grained materials. The cracks in the CPAWs firstly grow along the grain boundaries (Stage I crack growth, and then grow along the plane of maximum shear stress during the last stage of cycling (Stage II crack growth, leading to the distinctive fracture surfaces, i.e., the granular surface in the planar crack propagation region and the coarse fatigue striations in the 45°-inclined crack propagation region. The grain boundary migration was observed in the fatigued CPAWs. The increase in fatigue load enhances the dislocation recovery, increases the grain boundary migration rate, and thus promotes the occurrence of softening and damage localization up to the final failure.

  9. Computational Modeling to Predict Fatigue Behavior of NiTi Stents: What Do We Need?

    Directory of Open Access Journals (Sweden)

    Elena Dordoni

    2015-05-01

    Full Text Available NiTi (nickel-titanium stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of the device fatigue behavior is of primary importance to ensure a successful stenting procedure. Regulatory authorities recognize the possibility of performing computational analyses instead of experimental tests for the assessment of medical devices. However, confidence in numerical methods is only possible after verification and validation of the models used. For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process. Hence, special attention should be paid to the accuracy of the description of the device geometry and the material properties implementation into the numerical code, as well as to the definition of the fatigue limit. In this paper, a path for setting up an effective numerical model for NiTi stent fatigue assessment is proposed and the results of its application in a specific case study are illustrated.

  10. Effect of microstructure refinement on low cycle fatigue behavior of Alloy 718

    Directory of Open Access Journals (Sweden)

    Mukhtarov Shamil

    2014-01-01

    Full Text Available Microstructure refinement down to d ∼ 0.1–1 μm is known to enhance processing properties of hard-to-deform materials and particularly can be used for facilitating superplastic forming or roll-forming. However refined microstructure can compromise service properties, particularly fatigue properties. In the present work, the fatigue behavior of the fine-grained Alloy 718 has been investigated. A number of fine-grained conditions with a grain size ∼0.1–1 μm were produced using multiple forging with a graduate decrease of the forging temperature. Part of the forged fine-grained conditions was also subjected to conventional solution annealing and ageing. In this case a small grain size was controlled by precipitates of the δ phase located on grain boundaries. Low cycle fatigue tests of the fine-grained conditions were carried out at room and elevated temperatures. The obtained properties are compared with those of the Alloy 718 in the coarse-grained conditions. The effect of the grain size on the fatigue strength of the fine-grained Alloy 718 is discussed in terms of the microstructure evolution and fracture mode.

  11. Damage formation, fatigue behavior and strength properties of ZrO{sub 2}-based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Kozulin, A. A., E-mail: kozulyn@ftf.tsu.ru; Kulkov, S. S. [Tomsk State University, Tomsk, 634050 (Russian Federation); Narikovich, A. S.; Leitsin, V. N. [Immanuel Kant Baltic Federal University, Kaliningrad, 236041 (Russian Federation); Kulkov, S. N., E-mail: kulkov@ispms.ru [Tomsk State University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2016-08-02

    It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO{sub 2}-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91–0.98, 0.8–0.83, and 0.73–0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10{sup 5} stress cycles is in the range 33–34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

  12. Damage formation, fatigue behavior and strength properties of ZrO2-based ceramics

    Science.gov (United States)

    Kozulin, A. A.; Narikovich, A. S.; Kulkov, S. N.; Leitsin, V. N.; Kulkov, S. S.

    2016-08-01

    It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO2-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91-0.98, 0.8-0.83, and 0.73-0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 105 stress cycles is in the range 33-34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

  13. Relationships among the Microstructure, Mechanical Properties, and Fatigue Behavior in Thin Ti6Al4V

    Directory of Open Access Journals (Sweden)

    Y. Fan

    2016-01-01

    Full Text Available The microstructures of Ti6Al4V are complex and strongly affect its mechanical properties and fatigue behavior. This paper investigates the role of microstructure on mechanical and fatigue properties of thin-section Ti6Al4V sheets, with the aim of reviewing the effects of microstructure on fatigue properties where suboptimal microstructures might result following heat treatment of assemblies that may not be suited to further annealing, for example, following laser welding. Samples of Ti6Al4V sheet were subjected to a range of heat treatments, including annealing and water quenching from temperatures ranging from 650°C to 1050°C. Micrographs of these samples were inspected for microstructure, and hardness, 0.2% proof stress, elongation, and fracture strength were measured and attributed back to microstructure. Fractography was used to support the findings from microstructure and mechanical analyses. The strength ranking from high to low for the microstructures of thin Ti6Al4V sheets observed in this study is as follows: acicular α′ martensite, Widmanstätten, bimodal, and equiaxed microstructure. The fatigue strength ranking from high to low is as follows: equiaxed, bimodal, Widmanstätten, and acicular α′ martensite microstructure.

  14. Fatigue is a brain-derived emotion that regulates the exercise behavior to ensure the protection of whole body homeostasis

    Directory of Open Access Journals (Sweden)

    Timothy David Noakes

    2012-04-01

    Full Text Available An influential book written by A. Mosso in the late 19th century proposed that fatigue that at first sight might appear an imperfection of our body, is on the contrary one of its most marvellous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism so that muscular fatigue also is at bottom an exhaustion of the nervous system.It has taken more than a century to confirm Mosso’s idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso’s ideas were supplanted in the English literature by those of A.V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles - peripheral fatigue - to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance. This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops. These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop. The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body’s known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance.

  15. Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

    Institute of Scientific and Technical Information of China (English)

    Xue-xia Xu; Yang Yu; Wen-long Cui; Bing-zhe Bai; Jia-lin Gu

    2009-01-01

    The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite (CFB/M) complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a fre-quency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 107 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fa-tigue cycle exceeds 107 , and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of "soft structure". It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fa-tigue mechanism was discussed and it is suggested that specific CFB/M complex microstrueture of the studied steel contributes to itssuperior properties.

  16. Investigation of the effect of vacuum environment on the fatigue and fracture behavior of 7075-T6.

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

    Axial-load fatigue-life, fatigue-crack propagation, and fracture-toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at air pressures ranging from 101 kN/sq m to 7 micronewtons/sq m to determine the effect of air pressure on fatigue behavior. Analysis of the results from the fatigue-life experiments indicated that for a given stress level, the lower the air pressure was the longer the fatigue life. At a pressure of 7 micronewtons/sq m, fatigue lives were 15 to 30 times longer than at 101 kN/sq m. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue-crack-growth rates were approximately twice as high at atmospheric pressure as in vacuum. However, at higher values of stress-intensity range, the fatigue-crack-growth rates were nominally the same in vacuum and at atmospheric pressure.

  17. Deformation and fatigue behavior of SSME turbopump blade materials

    Science.gov (United States)

    Milligan, Walter W.; Antolovich, Stephen D.

    1987-01-01

    Directionally solidified and single crystal superalloys which are intended for use as turbopump blade materials are anisotropic both elastically and plastically. Therefore, isotropic constitutive models must be modified. Several models which are now being developed are based on metallurgical theories of deformation in these types of alloys. However, these theories have not been fully justified, and the temperature and strain regimes over which they may be valid are poorly defined. The objective of this work is to study the deformation behavior of the alloys, in order to determine the validity of these models and to thereby support the ongoing research efforts in solid mechanics.

  18. Thermomechanical Fatigue Behavior of the Intermetallic γ-TiAl Alloy TNB-V5 with Different Microstructures

    Science.gov (United States)

    Roth, Marcel; Biermann, Horst

    2010-03-01

    The cyclic deformation and fatigue behavior of the γ-TiAl alloy TNB-V5 is evaluated under thermomechanical load for three different microstructures. For this purpose, strain-controlled thermomechanical fatigue (TMF) tests were carried out with different temperature-strain cycles, different temperature ranges from 400 °C to 800 °C (673 K to 1073 K), and with two different strain ranges to set a fatigue-life relation. Cyclic deformation curves, stress-strain hysteresis loops, and fatigue lives of the tests are presented. The microstructures near-gamma (NG) and duplex (DP) show comparable fatigue lives under all test parameters. The microstructure fully-lamellar (FL) offers longer fatigue lives at the same loading conditions. For a general life prediction, the damage parameter of Smith, Watson, and Topper, P SWT vs fatigue life, is well suitable, if the testing and the application temperature ranges, respectively, include temperatures above the ductile-brittle transition (approximately 750 °C). In the completely brittle material behavior regime the quality of the lifetime prediction is unacceptable. The damage parameter P HL by Haibach and Lehrke shows a comparable correlation to the fatigue life as P SWT. The results are discussed with microstructural investigations.

  19. Effect of corrosion and sandblasting on the high cycle fatigue behavior of reinforcing B500C steel bars

    Directory of Open Access Journals (Sweden)

    Marina C. Vasco

    2017-10-01

    Full Text Available . In a series of applications, steel reinforced concrete structures are subjected to fatigue loads during their service life, what in most cases happens in corrosive environments. Surface treatments have been proved to represent proper processes in order to improve both fatigue and corrosion resistances. In this work, the effect of corrosion and sandblasting on the high cycle fatigue behavior reinforcing steel bars is investigated. The investigated material is the reinforcing steel bar of technical class B500C, of nominal diameter of 12 mm. Steel bars specimens were first exposed to corrosion in alternate salt spray environment for 30 and 60 days and subjected to both tensile and fatigue tests. Then, a series of specimens were subjected to common sandblasting, corroded and mechanically tested. Metallographic investigation and corrosion damage evaluation regarding mass loss and martensitic area reduction were performed. Tensile tests were conducted after each corrosion exposure period prior to the fatigue tests. Fatigue tests were performed at a stress ratio, R, of 0.1 and loading frequency of 20 Hz. All fatigue tests series as well as tensile test were also performed for as received steel bars to obtain the reference behavior. The results have shown that sandblasting hardly affects the tensile behavior of the uncorroded material. The effect of sandblasting on the tensile behavior of pre-corroded specimens seems to be also limited. On the other hand, fatigue results indicate an improved fatigue behavior for the sandblasted material after 60 days of corrosion exposure. Martensitic area reductions, mass loss and depth of the pits were significantly smaller for the case of sandblasted materials, which confirms an increased corrosion resistance

  20. Comportamiento a fatiga del vástago de una prótesis para cadera al caminar//Fatigue behavior stem hip prosthesis for walking

    Directory of Open Access Journals (Sweden)

    Ángel Martínez-Delfín

    2014-01-01

    Full Text Available La prótesis de cadera consiste en sustituir la parte superior fracturada del fémur por una pieza de material biocompatible. Debido a las cargas aleatorias que sobre esta prótesis actúan al caminar la persona injertada, surge la fatiga sobre la prótesis. En este trabajo se realiza el cálculo a fatiga del vástago de una prótesis de caderas fabricada con acero inoxidable austenítico AISI 316L GrQ y de uso actual. Para ellose emplea el método de los elementos finitos, considerando la compleja geometría del vástago, el material y las cargas variables resultantes del caminar de la persona con la prótesis artificial colocada. Se calcula el daño a fatiga que estas cargas provocan en la misma así como el número de pasos que pueden darse, garantizándose una larga vida útil de la prótesis por este concepto de resistencia.Palabras claves: fatiga, prótesis de cadera, ciclo, daño, elementos finitos.______________________________________________________________________________AbstractThe hip prosthesis consists in substituting the fractured femur part by a piece of biocompatible material. Because the random character of loads acting over this prosthesis while person walk, crop up the fatigue on the prosthesis. The fatigue behavior of austenitic stainless steel hips prosthesis is studied in this article. The method of finite elements is used, considering the complex geometry of the part, the material and the variable acting loads, as results of steps of walking person. The fatigue damages are calculated as well as the number of steps that can be given, guarantying a long life of the prosthesis for fatigue resistance concept.Key words: fatigue, hip prosthesis, cycle, damage, finite elements.

  1. Association of fatigue with emotional-eating behavior and the response to mental stress in food intake in a young adult population.

    Science.gov (United States)

    Yoshikawa, Takahiro; Tanaka, Masaaki; Ishii, Akira; Watanabe, Yasuyoshi

    2014-01-01

    Fatigue is a common complaint among young adults. We investigated whether eating behaviors are associated with fatigue in this population. The participants consisted of 117 healthy students attending Osaka City University. They completed questionnaires assessing fatigue and eating behaviors. To identify the factors associated with the prevalence of fatigue, multivariate logistic regression analysis adjusted for gender was performed. The Emotional Eating subscale score of the Japanese version of Three-Factor Eating Questionnaire Revised 21-item and stress response in food intake (large decrease vs. no change) were positively associated with the prevalence of fatigue assessed by the Japanese version of the Chalder Fatigue Scale. The finding suggests that emotional eating and decrease in amount of food intake under mental stress were associated with fatigue in healthy young adults. Our findings may help to clarify the mechanisms underlying fatigue-eating coupling as well as the etiology of diseases related to abnormal eating behavior.

  2. Isothermal fatigue behavior and damage modeling of a high temperature woven PMC[Polymer Matrix Composite

    Energy Technology Data Exchange (ETDEWEB)

    Gyekenyesi, A.L.

    2000-01-01

    This study focuses on the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed greater reductions due to the elevated temperature. The stiffness degradation as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment covering the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

  3. The development of thermal fatigue test facility to evaluate fatigue behavior for nozzle header of one-through helical steam geneator

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Y. H.; Kim, J. I. [KAERI, Taejon (Korea, Republic of); Lee, H. S. [Hyundai Titanium Co., LTD, Inchon (Korea, Republic of)

    2001-05-01

    Nozzle header of SMART steam generator is subjected to severe thermal transient loading induced by the temperature difference between primary coolant and secondary coolant. In this study, thermal fatigue test facility was developed to characterize the fatigue behavior of the nozzle header. The temperature and the pressure of the primary coolant loop is controled by the heaters installed in the pressurizer and test vessel. The thermo-hydraulic parameters of the secondary system are adjusted by the expansion tank and the heat exchanger, Strain gages and thermocouples are installed at the high stressed position of nozzle header. In this test facility, real time monitoring of the strain and the temperature of nozzle header is possible utilizing the data acquisition system. Fatigue test plan for the nozzle header has been established based on the operation strategy of the integral reactor SMART.

  4. Tribological and Impact Fatigue Behaviors of Pure Titanium Treated by Plasma Ni Alloying

    Institute of Scientific and Technical Information of China (English)

    WANG Zhenxia; HE Zhiyong; WANG Yingqin; LIU Xiaoping; TANG Bin

    2012-01-01

    Ni modified layer is prepared on the surface of pure titanium by plasma surface alloying technique.Surface appearance,micro-structure morphology,composition distribution,phase structure and microhardness of Ni modified layer are analyzed.Tribological performance and fatigue behaviors of Ni modified layer of pure titanium are observed using Pin-on-disc tribometer and repeated impact test.The results indicate that the surface mean Ni concentration of Ni modified layer is nearly 18% which is composed of TiNi,Ti2Ni and Ti phase.The maximum surface microhardness of Ni modified layer is approximately 580 HV which is almost two-fold of the hardness of the substrate.The wear resistance of Ni modified layer is improved obviously.The wear mechanism of Ni modified layer shows slight abrasion wearing,while pure titanium is abrasion and adhesion wearing.Ni modified layer presents better impact fatigue strength.

  5. Delamination growth behavior in cross-ply composites under compressive cyclic (fatigue) loading

    Science.gov (United States)

    Pelegri, Assimina A.

    A mode dependent fatigue delamination growth law for anisotropic composite plates is presented in this thesis. The novelty of the presented law lies in the mode dependency of the material and laminate constants m(Psi) and C(Psi). The model describing the mode dependent delamination growth law consists of an initial postbuckling solution accounting for general delaminated composites, i.e. with no restrictive assumptions on the delamination dimensions, and a fracture mechanics solution. A numerical code was developed for the implementation of the closed form solution which gives the loading and geometrical quantities as well as the energy release rates and the mode mixities. The computer code was especially designed for parametric studies. Parameters assigned in this particular investigation were: end conditions, delamination position (h/T), and applied strain. The effect of the end conditions, i.e. clamped-clamped versus simply-supported ends on the initial postbuckling and growth behavior of delaminated plates was also investigated. In conjunction with the previous analysis, a detailed experimental study was designed and carried out in order to validate the proposed model. The tests were designed so that the effect of certain parameters on the delamination growth behavior could be evaluated. The parameters included in the investigation were: initial delamination length, applied strain and delamination position (h/T). Compressive static, compressive fatigue (constant displacement amplitude), and double cantilever beam (DCB) tests were conducted. Data acquisition and analysis for these tests were performed. By comparing analytical and experimental results it is shown that a very good correlation exists, and the presented mode dependent fatigue delamination growth law can accurately predict fatigue lives of delaminated composite structures.

  6. Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

    Institute of Scientific and Technical Information of China (English)

    XUE Hong-qian; TAO Hua; SHAO Ren-ping; B.CLAUDE

    2008-01-01

    A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 1010 cycles and associated fracture behavior of Ti-Al alloy. Tests were performed at a frequency of 20kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect of surface roughness on fatigue life. Furthermore, optical microscopy (OM) and scanning electron microscopy (SEM) were used for microstructure characteristic and fracture surface analysis. The S-N curves obtained show that fatigue failure occurs in the range of 105-1010 cycles, and the asymptote of S-N curve inclines slightly in very high cycle regime, but is not horizontal for R=0.5. Fatigue limit appears after 108 cycles for R=0.7. Surface roughness (the maximum roughness is no more than 3μm) has no influence on the fatigue properties in the high cycle regime. A detailed investigation on fatigue fracture surface shows that the Ti-Al alloy studied here is a binary alloy in the microstructure composed of α2-Ti3Al and γ-Ti-Al with fully lamellar microstructure. Fractography shows that fatigue failures are mostly initiated on the surface of specimens, also, in very high cycle regime, subsurface fatigue crack initiation can be found. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with fully lamellar structure. Fatigue crack growth is mainly in transgranular mode.

  7. Effects of temperature, slip amplitude, contact pressure on fretting fatigue behavior of Ti811 alloys at elevated temperatures

    Institute of Scientific and Technical Information of China (English)

    Xiaohua ZHANG; Daoxin LIU

    2009-01-01

    Effects of the temperature, slip amplitude, and contact pressure on fretting fatigue (FF) behavior of the Ti811 titanium alloy were investigated using a high frequency fatigue machine and a home-made high temperature apparatus. The fretting fatigue failure mechanism was studied by observing the fretting surface morphology features. The results show that the sensitivity to fretting fatigue is high at both 350 and 500 ℃. The higher the temperature, the more sensitive to the fretting fatigue failure is. Creep is an important factor that influences the fretting fatigue failure process at elevated temperatures. The fretting fatigue life of the Ti811 alloy does not change in a monotonic way as the slip amplitude and contact pressure increase. This is owing to the fact that the slip amplitude affects the action of fatigue and wear in the fretting process, and the nominal contact pressure affects the distribution and concentration of the stress and the amplitude of fretting slip at the contact surface, and thus further influences the crack initiation probability and the driving force for propagation.

  8. Behavior-based network management: a unique model-based approach to implementing cyber superiority

    Science.gov (United States)

    Seng, Jocelyn M.

    2016-05-01

    Behavior-Based Network Management (BBNM) is a technological and strategic approach to mastering the identification and assessment of network behavior, whether human-driven or machine-generated. Recognizing that all five U.S. Air Force (USAF) mission areas rely on the cyber domain to support, enhance and execute their tasks, BBNM is designed to elevate awareness and improve the ability to better understand the degree of reliance placed upon a digital capability and the operational risk.2 Thus, the objective of BBNM is to provide a holistic view of the digital battle space to better assess the effects of security, monitoring, provisioning, utilization management, allocation to support mission sustainment and change control. Leveraging advances in conceptual modeling made possible by a novel advancement in software design and implementation known as Vector Relational Data Modeling (VRDM™), the BBNM approach entails creating a network simulation in which meaning can be inferred and used to manage network behavior according to policy, such as quickly detecting and countering malicious behavior. Initial research configurations have yielded executable BBNM models as combinations of conceptualized behavior within a network management simulation that includes only concepts of threats and definitions of "good" behavior. A proof of concept assessment called "Lab Rat," was designed to demonstrate the simplicity of network modeling and the ability to perform adaptation. The model was tested on real world threat data and demonstrated adaptive and inferential learning behavior. Preliminary results indicate this is a viable approach towards achieving cyber superiority in today's volatile, uncertain, complex and ambiguous (VUCA) environment.

  9. Surface modification and fatigue behavior of nitinol for load bearing implants

    Science.gov (United States)

    Bernard, Sheldon A.

    Musculoskeletal disorders are recognized amongst the most significant human health problems that exist today. Even though considerable research and development has gone towards understanding musculoskeletal disorders, there is still lack of bone replacement materials that are appropriate for restoring lost structures and functions, particularly for load-bearing applications. Many materials on the market today, such as titanium and stainless steel, suffer from significantly higher modulus than natural bone and low bioactivity leading to stress shielding and implant loosening over longer time use. Nitinol (NiTi) is an equiatomic intermetallic compound of nickel and titanium whose unique biomechanical and biological properties contributed to its increasing use as a biomaterial. An innovative method for creating dense and porous net shape NiTi alloy parts has been developed to improve biological properties while maintaining comparable or better mechanical properties than commercial materials that are currently in use. Laser engineered net shaping (LENS(TM)) and surface electrochemistry modification was used to create dense/porous samples and micro textured surfaces on NiTi parts, respectively. Porous implants are known to promote cell adhesion and have a low elastic modulus, a combination that can significantly increase the life of an implant. However, porosity can significantly reduce the fatigue life of an implant, and very little work has been reported on the fatigue behavior of bulk porous metals, specifically on porous nitinol alloy. High-cycle rotating bending and compression-compression fatigue behavior of porous NiTi fabricated using LENS(TM) were studied. In cyclic compression loading, plastic strain increased with increasing porosity and it was evident that maximum strain was achieved during the first 50000 cycles and remained constant throughout the remaining loading. No failures were observed due to loading up to 150% of the yield strength. When subjected

  10. The significance of ultrafine film-like retained austenite in governing very high cycle fatigue behavior in an ultrahigh-strength MN–SI–Cr–C steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, P., E-mail: zhaoping12@mails.tsinghua.edu.cn [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Zhang, B.; Cheng, C. [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Misra, R.D K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968-0520 (United States); Gao, G., E-mail: gaogh@bjtu.edu.cn [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Bai, B.; Weng, Y. [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China)

    2015-10-01

    We elucidate here the very high cycle fatigue (VHCF) behavior of an ultrahigh-strength medium carbon Mn–Si–Cr–C steel processed using the approach of bainite-based quenching and partitioning (BQ&P). The microstructure of BQ&P process comprised of bainite, carbon-depleted martensite, retained austenite (RA) and small amount of martensite/austenite island (M/A). The tensile strength (R{sub m}) and fatigue limit strength after 10{sup 9} cycles (σ{sub w9}) and in the non-failed condition were 1688 MPa and 875 MPa, respectively such that σ{sub w9}/R{sub m} exceeded conventional steels and was 0.52. Two types of failure modes were observed depending on the surface and microstructure, notably surface-induced failure and non-inclusion-induced failure, where the non-inclusion-induced failure was influenced by the microstructure. Inclusion-induced failure was absent. The study underscores that film-like retained austenite was the underlying reason for superior fatigue properties, hitherto not previously obtained.

  11. Cognitive Behavior Therapy to Treat Sleep Disturbance and Fatigue After Traumatic Brain Injury: A Pilot Randomized Controlled Trial.

    Science.gov (United States)

    Nguyen, Sylvia; McKay, Adam; Wong, Dana; Rajaratnam, Shantha M; Spitz, Gershon; Williams, Gavin; Mansfield, Darren; Ponsford, Jennie L

    2017-08-01

    To evaluate the efficacy of adapted cognitive behavioral therapy (CBT) for sleep disturbance and fatigue in individuals with traumatic brain injury (TBI). Parallel 2-group randomized controlled trial. Outpatient therapy. Adults (N=24) with history of TBI and clinically significant sleep and/or fatigue complaints were randomly allocated to an 8-session adapted CBT intervention or a treatment as usual (TAU) condition. Cognitive behavior therapy. The primary outcome was the Pittsburgh Sleep Quality Index (PSQI) posttreatment and at 2-month follow-up. Secondary measures included the Insomnia Severity Index, Fatigue Severity Scale, Brief Fatigue Inventory (BFI), Epworth Sleepiness Scale, and Hospital Anxiety and Depression Scale. At follow-up, CBT recipients reported better sleep quality than those receiving TAU (PSQI mean difference, 4.85; 95% confidence interval [CI], 2.56-7.14). Daily fatigue levels were significantly reduced in the CBT group (BFI difference, 1.54; 95% CI, 0.66-2.42). Secondary improvements were significant for depression. Large within-group effect sizes were evident across measures (Hedges g=1.14-1.93), with maintenance of gains 2 months after therapy cessation. Adapted CBT produced greater and sustained improvements in sleep, daily fatigue levels, and depression compared with TAU. These pilot findings suggest that CBT is a promising treatment for sleep disturbance and fatigue after TBI. Copyright © 2017 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

  12. Behavior of sandwich panels subjected to bending fatigue, axial compression loading and in-plane bending

    Science.gov (United States)

    Mathieson, Haley Aaron

    This thesis investigates experimentally and analytically the structural performance of sandwich panels composed of glass fibre reinforced polymer (GFRP) skins and a soft polyurethane foam core, with or without thin GFRP ribs connecting skins. The study includes three main components: (a) out-of-plane bending fatigue, (b) axial compression loading, and (c) in-plane bending of sandwich beams. Fatigue studies included 28 specimens and looked into establishing service life (S-N) curves of sandwich panels without ribs, governed by soft core shear failure and also ribbed panels governed by failure at the rib-skin junction. Additionally, the study compared fatigue life curves of sandwich panels loaded under fully reversed bending conditions (R=-1) with panels cyclically loaded in one direction only (R=0) and established the stiffness degradation characteristics throughout their fatigue life. Mathematical models expressing fatigue life and stiffness degradation curves were calibrated and expanded forms for various loading ratios were developed. Approximate fatigue thresholds of 37% and 23% were determined for non-ribbed panels loaded at R=0 and -1, respectively. Digital imaging techniques showed significant shear contribution significantly (90%) to deflections if no ribs used. Axial loading work included 51 specimens and examined the behavior of panels of various lengths (slenderness ratios), skin thicknesses, and also panels of similar length with various rib configurations. Observed failure modes governing were global buckling, skin wrinkling or skin crushing. In-plane bending involved testing 18 sandwich beams of various shear span-to-depth ratios and skin thicknesses, which failed by skin wrinkling at the compression side. The analytical modeling components of axially loaded panels include; a simple design-oriented analytical failure model and a robust non-linear model capable of predicting the full load-displacement response of axially loaded slender sandwich panels

  13. Low Cycle Fatigue behavior of SMAW welded Alloy28 superaustenitic stainless steel at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kchaou, Y., E-mail: yacinekchaou@yahoo.fr [Institut Pprime, Département Physique et Mécanique des Matériaux, UPR 3346 CNRS ISAE-ENSMA Université de Poitiers, Téléport 2, 1, avenue Clément Ader, BP 40109, F – 86961 Futuroscope Chasseneuil Cedex (France); Laboratoire de Génie des Matériaux et Environnement (LGME), ENIS, BPW 1173, Sfax (Tunisia); Pelosin, V.; Hénaff, G. [Institut Pprime, Département Physique et Mécanique des Matériaux, UPR 3346 CNRS ISAE-ENSMA Université de Poitiers, Téléport 2, 1, avenue Clément Ader, BP 40109, F – 86961 Futuroscope Chasseneuil Cedex (France); Haddar, N.; Elleuch, K. [Laboratoire de Génie des Matériaux et Environnement (LGME), ENIS, BPW 1173, Sfax (Tunisia)

    2016-01-10

    This paper focused on the study of Low Cycle Fatigue of welded joints of superaustenitic (Alloy28) stainless steels. Chemical composition and microstructure investigation of Base Metal (BM) and Weld Metal (WM) were identified. The results showed that both of composition is fully austenitic with a dendritic microstructure in the WM. Low cycle fatigue tests at different strain levels were performed on Base Metal (BM) and Welded Joint (WJ) specimens with a strain ratio R{sub ε}=−1. The results indicated that the fatigue life of welded joints is lower than the base metal. This is mainly due to the low ductility of the Welded Metal (WM) and the presence of welding defects. Simultaneously, Scanning Electron Microscope (SEM) observations of fractured specimens show that WJ have brittle behavior compared to BM with the presence of several welding defects especially in the crack initiation site. An estimation of the crack growth rate during LCF tests of BM and WJ was performed using distance between striations. The results showed that the crack initiation stage is shorter in the case of WJ compared to BM because of the presence of welding defects in WJ specimens.

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

    Science.gov (United States)

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

    1985-01-01

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

  15. Fatigue behavior of superferritic stainless steel laser shock treated without protective coating

    Science.gov (United States)

    Spadaro, L.; Gomez-Rosas, G.; Rubio-González, C.; Bolmaro, R.; Chavez-Chavez, A.; Hereñú, S.

    2017-08-01

    The laser shock peening (LSP) is a new technique that improves the fatigue life of metallic components by inducing deep compressive residual stresses through the surface. However, the beneficial effects of LSP depend on the persistence and stability of such residual stress fields under cyclic loading and temperature. Moreover, if no absorbent coating is used in LSP operation, thermal effects can occur on the metallic substrate. The purpose of this work is to study the influence of LSP, without protective coating and with different pulse densities, on the low cyclic fatigue behavior of a superferritic stainless steel UNS S 44600. These results are correlated with observations performed by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with electron diffraction spectroscopy (EDS). The hole-drilling method is used to measure residual stresses. The micro-hardness and roughness profiles are also presented. This paper shows that LSP without coating produces beneficial compression residual stresses. However, in the first 10 μm beneath the surface, thermal effects occur that induce intergranular corrosion. This intergranular corrosion deteriorates the fatigue properties of a superferritic stainless steel UNS S 44600.

  16. Dwell Notch Low Cycle Fatigue Behavior of a Powder Metallurgy Nickel Disk Alloy

    Science.gov (United States)

    Telesman, J.; Gabb, T. P.; Yamada, Y.; Ghosn, L. J.; Jayaraman, N.

    2012-01-01

    A study was conducted to determine the processes which govern dwell notch low cycle fatigue (NLCF) behavior of a powder metallurgy (P/M) ME3 disk superalloy. The emphasis was placed on the environmentally driven mechanisms which may embrittle the highly stressed notch surface regions and reduce NLCF life. In conjunction with the environmentally driven notch surface degradation processes, the visco-plastic driven mechanisms which can significantly change the notch root stresses were also considered. Dwell notch low cycle fatigue testing was performed in air and vacuum on a ME3 P/M disk alloy specimens heat treated using either a fast or a slow cooling rate from the solutioning treatment. It was shown that dwells at the minimum stress typically produced a greater life debit than the dwells applied at the maximum stress, especially for the slow cooled heat treatment. Two different environmentally driven failure mechanisms were identified as the root cause of early crack initiation in the min dwell tests. Both of these failure mechanisms produced mostly a transgranular crack initiation failure mode and yet still resulted in low NLCF fatigue lives. The lack of stress relaxation during the min dwell tests produced higher notch root stresses which caused early crack initiation and premature failure when combined with the environmentally driven surface degradation mechanisms. The importance of environmental degradation mechanisms was further highlighted by vacuum dwell NLCF tests which resulted in considerably longer NLCF lives, especially for the min dwell tests.

  17. A preliminary characterization of the tensile and fatigue behavior of tungsten-fiber/Waspaloy-matrix composite

    Science.gov (United States)

    Corner, Ralph E.; Lerch, Brad A.

    1992-01-01

    A microstructural study and a preliminary characterization of the room temperature tensile and fatigue behavior of a continuous, tungsten fiber, Waspaloy-matrix composite was conducted. A heat treatment was chosen that would allow visibility of planar slip if it occurred during deformation, but would not allow growth of the reaction zone. Tensile and fatigue tests showed that the failed specimens contained transverse cracks in the fibers. The cracks that occurred in the tensile specimen were observed at the fracture surface and up to approximately 4.0 mm below the fracture surface. The crack spacing remained constant along the entire length of the cracked fibers. Conversely, the cracks that occurred in the fatigue specimen were only observed in the vicinity of the fracture surface. In instances where two fiber cracks occurred in the same plane, the matrix often necked between the two cracked fibers. Large groups of slip bands were generated in the matrix near the fiber cracks. Slip bands in the matrix of the tensile specimen were also observed in areas where there were no fiber cracks, at distances greater than 4 mm from the fracture surface. This suggests that the matrix plastically flows before fiber cracking occurs.

  18. The Effects of Hot Bending on the Low Cycle Fatigue Behaviors of 347 SS in PWR Primary Environment

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ho-Sub; Hong, Jong-Dae; Lee, Junho; Jang, Changheui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-10-15

    Fatigue damage could be significant for some locations, especially the welds and bends where stress concentration is typically high. As a possible solution, a large radius hot-bending method has been suggested to eliminate some weld joints and all tight bends. However, for the hot-bending process which involves a high temperature thermal cycle, there is a concern about changes in mechanical properties including low cycle fatigue behaviors. In APR1400, Type 347 SS have been used as surge line pipes. Therefore, to verify the applicability of hot-bending on 347 SS surge line pipes, an environmental fatigue test program was initiated. In this paper, the preliminary results of the on-going test program are introduced. Also, the low cycle fatigue behaviors of 347 SS are compared with those of other grade of stainless steels. The effects of hot bending on the low cycle fatigue behavior of 347 SS were quantitatively evaluated. The fatigue life was compared with the estimated values per NUREG 6909 rev. 1. There are no distinct differences between NUREG 6909 and LCF tests. According to fractography and cross section analysis in progress, basically, the reduction of LCF life of 347 SS in PWR water was caused by operation of HIC mechanism. The cyclic stress responses shows that there is no secondary hardening in 330 .deg.C air and PWR water.

  19. On the fatigue behavior of medical Ti6Al4V roughened by grit blasting and abrasiveless waterjet peening.

    Science.gov (United States)

    Lieblich, M; Barriuso, S; Ibáñez, J; Ruiz-de-Lara, L; Díaz, M; Ocaña, J L; Alberdi, A; González-Carrasco, J L

    2016-10-01

    Flat fatigue specimens of biomedical Ti6Al4V ELI alloy were surface-processed by high pressure waterjet peening (WJP) without abrasive particles using moderate to severe conditions that yield roughness values in the range of those obtained by commercial grit blasting (BL) with alumina particles. Fatigue behavior of WJP and BL specimens was characterized under cyclical uniaxial tension tests (R=0.1). The emphasis was put on a comparative analysis of the surface and subsurface induced effects and in their relevance on fatigue behavior. Within the experimental setup of this investigation it resulted that blasting with alumina particles was less harmful for fatigue resistance than abrasiveless WJP. BL specimens resulted in higher subsurface hardening and compressive residual stresses. Specimens treated with more severe WJP parameters presented much higher mass loss and lower compressive residual stresses. From the analysis performed in this work, it follows that, in addition to roughness, waviness emerges as another important topographic parameter to be taken into account to try to predict fatigue behavior. It is envisaged that optimization of WJP parameters with the aim of reducing waviness and mass loss should lead to an improvement of fatigue resistance.

  20. Low Cycle Fatigue Behavior of Conventionally Cast MAR-M 200 at 1000 C.

    Science.gov (United States)

    1984-09-01

    propagation, as illustrated in figures 5 and 6. Gell and Leverant (ref. 1), McMahon and Coffin (ref. 7), Coffin (ref. 8), and Antolovich , Liu and Baur (ref...propagation in Rene’ 80 was primarily transgranular, independent of cyclic loading frequency. Antolovich et. al. reported crack initiation in Rene’ 80 at...on the Cyclic Strain and Fatigue Behavior of Cast Rene’ at 16000 F. Metall. Trans., vol. 5, 1974, no. 5, May pp 1053-1060. 9. Antolovich , Stephen 0

  1. Cyclic-Tension Fatigue Behavior in a SS400 Steel Plate Studied Using Ultrasonic Linear and Nonlinear Techniques

    Science.gov (United States)

    Yamagishi, Hideki; Fukuhara, Mikio

    2015-11-01

    Three acoustic probe configurations were used to assess cyclic-tension fatigue in SS400 steel at room temperature via a diffracted horizontally polarized shear wave (SH) transmission method. Linear analysis of the propagation time and amplitude of shear and longitudinal waves with fatigue progression revealed that the linear behavior was governed by residual stress, attributed to the acoustoelastic effect. Specifically, the propagation time of the shear waves increased and the wave amplitude decreased with fatigue progression. Our results also revealed that the propagation paths of the waves became deeper with progressive fatigue. Additionally, when the probe angle was optimized for diffraction, the estimated change in the length prior to fatigue breakage was 0.61 pct. Nonlinear analysis results revealed that second harmonic β-parameters increased as fatigue progressed, up to ~800 pct for the optimal frequency configuration; this was attributed to an increase in the number of dislocation-associated viscoelastic effects. The proposed approach shows great potential for nondestructive evaluation of metal fatigue via parameter analysis of residual stress and dislocation variations.

  2. Effects of WC-17Co Coating Combined with Shot Peening Treatment on Fatigue Behaviors of TC21 Titanium Alloy

    Directory of Open Access Journals (Sweden)

    Dongxing Du

    2016-10-01

    Full Text Available The improvement and mechanism of the fatigue resistance of TC21 high-strength titanium alloy with a high velocity oxygen fuel (HVOF sprayed WC-17Co coating was investigated. X-ray diffraction (XRD and the corresponding stress measurement instrument, a surface roughness tester, a micro-hardness tester, and a scanning electron microscope (SEM were used to determine the properties of the HVOF WC-17Co coating with or without shot peening. The fatigue behavior of the TC21 titanium alloy with or without the WC-17Co coating was determined by using a rotating bending fatigue testing machine. The results revealed that the polished HVOF sprayed WC-17Co coating had almost the same fatigue resistance as the TC21 titanium alloy substrate. This resulted from the polishing-induced residual surface compressive stress and a decrease in the stress concentration on the surface of the coating. Moderate-intensity shot peening of the polished WC-17Co coatings resulted in significant improvement of the fatigue resistance of the alloy. Furthermore, the fatigue life was substantially higher than that of the substrate, owing to the deep distribution of residual stress and high compressive stress induced by shot peening. The improved surface toughness of the coating can effectively delay the initiation of fatigue crack propagation.

  3. Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

    Science.gov (United States)

    Mehmood, Shahid; Shah, Masood; Pasha, Riffat Asim; Sultan, Amir

    2017-09-01

    The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

  4. Corrosion Fatigue Behavior of 316LN SS in Acidified Sodium Chloride Solution at Applied Potential

    Science.gov (United States)

    Poonguzhali, A.; Pujar, M. G.; Mallika, C.; Mudali, U. Kamachi

    2015-05-01

    The influence of acidified 1 M NaCl solution by addition of 2 ml/L of HCl on the cyclic plastic deformation of AISI Type 316LN SS containing 0.07 wt.% and 0.22 wt.% N was investigated as a function of the applied potentials. The corrosion fatigue (CF) behavior of stainless steel (SS) was explained vis-a-vis the dislocation behavior, the propensity to form microcracks, and the evolution of the current transients based on the studies carried out at both room-temperature and boiling conditions. CF experiments were conducted using round tensile specimens at a stress ratio of 0.5 and a frequency of 0.1 Hz. Two different kinds of damage mechanisms were observed (I) the damage mechanism in the stable-passive state was correlated with the localization of the anodic dissolution due to a depassivation-repassivation process, whereas (II) the cyclic stress induced pitting corrosion in the metastable pitting state, which resulted in formation of microcracks. The study of the microcracking process and its evolution is a key to the physical mechanism by which the fatigue life of stainless steels would be affected in an aqueous corrosive solution under the applied potential.

  5. Fatigue Hardening Behavior of 1.5 GPa Grade Transformation-Induced Plasticity-Aided Martensitic Steel

    Science.gov (United States)

    Sugimoto, Koh-Ichi; Hojo, Tomohiko

    2016-11-01

    Low cycle fatigue hardening/softening behavior of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-1.0 pct Cr-0.2 pct Mo-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel consisting of a wide lath martensite structure matrix and a narrow lath martensite-metastable retained austenite mixture was investigated. The steel exhibited notable fatigue hardening in the same way as TRIP-aided bainitic ferrite steel, although conventional martensitic steel such as SCM420 steel with the same tensile strength exhibited fatigue softening. The considerable fatigue hardening of this steel is believed to be associated mainly with the compressive internal stress that results from a difference in flow stress between the matrix and the martensite-austenite-like phase, with a small contribution from the strain-induced transformation and dislocation hardenings.

  6. High temperature tension-compression fatigue behavior of a tungsten copper composite

    Science.gov (United States)

    Verrilli, Michael J.; Gabb, Timothy P.

    1990-01-01

    The high temperature fatigue of a (O)12 tungsten fiber reinforced copper matrix composite was investigated. Specimens having fiber volume percentages of 10 and 36 were fatigued under fully-reversed, strain-controlled conditions at both 260 and 560 C. The fatigue life was found to be independent of fiber volume fraction because fatigue damage preferentially occurred in the matrix. Also, the composite fatigue lives were shorter at 560 C as compared to 260 C due to changes in mode of matrix failure. On a total strain basis, the fatigue life of the composite at 560 C was the same as the life of unreinforced copper, indicating that the presence of the fibers did not degrade the fatigue resistance of the copper matrix in this composite system. Comparison of strain-controlled fatigue data to previously-generated load-controlled data revealed that the strain-controlled fatigue lives were longer because of mean strain and mean stress effects.

  7. Creep-Fatigue Behavior of Alloy 617 at 850°C

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, Laura [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-05-01

    Creep-fatigue deformation is expected to be a significant contributor to the potential factors that limit the useful life of the Intermediate Heat Exchanger (IHX) in the Very High Temperature Reactor (VHTR) nuclear system.[1] The IHX of a high temperature gas reactor will be subjected to a limited number of transient cycles due to start-up and shut-down operations imparting high local stresses on the component. This cycling introduces a creep-fatigue type of interaction as dwell times occur intermittently. The leading candidate alloy for the IHX is a nickel-base solid solution strengthened alloy, Alloy 617, which must safely operate near the expected reactor outlet temperature of up to 950 °C.[1] This solid solution strengthened nickel-base alloy provides an interesting creep-fatigue deformation case study because it has characteristics of two different alloy systems for which the cyclic behavior has been extensively investigated. Compositionally, it resembles nickel-base superalloys, such as Waspalloy, IN100, and IN718, with the exception of its lower levels of Al. At temperatures above 800 °C, the microstructure of Alloy 617, however, does not contain the ordered ?’ or ?’’ phases. Thus microstructurally, it is more similar to an austenitic stainless steel, such as 316 or 304, or Alloy 800H comprised of a predominantly solid solution strengthened matrix phase with a dispersion of inter- and intragranular carbides. Previous studies of the creep-fatigue behavior of Alloy 617 at 950 °C indicate that the fatigue life is reduced when a constant strain dwell is added at peak tensile strain.[2-5] This results from the combination of faster crack initiation occurring at surface-connected grain boundaries due to oxidation from the air environment along with faster, and intergranular, crack propagation resulting from the linking of extensive interior grain boundary cracking.[3] Saturation, defined as the point at which further increases in the strain

  8. Stress-related psychosocial factors at work, fatigue, and risky driving behavior in bus rapid transport (BRT) drivers.

    Science.gov (United States)

    Useche, Sergio A; Ortiz, Viviola Gómez; Cendales, Boris E

    2017-07-01

    There is consistent scientific evidence that professional drivers constitute an occupational group that is highly exposed to work related stressors. Furthermore, several recent studies associate work stress and fatigue with unsafe and counterproductive work behaviors. This study examines the association between stress-related work conditions of Bus Rapid Transport (BRT) drivers and risky driving behaviors; and examines whether fatigue is a mechanism that mediates the association between the two. A sample of 524 male Bus Rapid Transit (BRT) operators were drawn from four transport companies in Bogotá, Colombia. The participants answered a survey which included an adapted version of the Driver Behavior Questionnaire (DBQ) for BRT operators, as well as the Effort-Reward Imbalance and Job Content Questionnaires, the Subjective Fatigue subscale of the Checklist Individual Strength (CIS) and the Need for Recovery after Work Scale (NFR). Utilizing Structural Equation Models (SEM) it was found that risky driving behaviors in BRT operators could be predicted through job strain, effort-reward imbalance and social support at work. It was also found that fatigue and need for recovery fully mediate the associations between job strain and risky driving, and between social support and risky driving, but not the association between effort/reward imbalance (ERI) and risky driving. The results of this study suggest that a) stress related working conditions (Job Strain, Social Support and ERI) are relevant predictors of risky driving in BRT operators, and b) that fatigue is the mechanism which links another kind of stress related to working conditions (job strain and low social support) with risky driving. The mechanism by which ERI increases risky driving in BRT operators remains unexplained. This research suggests that in addition to the individual centered stress-reduction occupational programs, fatigue management interventions aimed to changing some working conditions may reduce

  9. Effect of fiber fabric orientation on the flexural monotonic and fatigue behavior of 2D woven ceramic matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Chawla, N., E-mail: nchawla@asu.edu [Materials Science and Engineering, Arizona State University Tempe, AZ 85287-6106 (United States); Liaw, P.K. [Department of Materials Science and Engineering, University of Tennessee-Knoxville, Knoxville, TN 37996 (United States); Lara-Curzio, E.; Ferber, M.K.; Lowden, R.A. [High Temperature Materials Laboratory, Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States)

    2012-11-15

    The effect of fiber fabric orientation, i.e., parallel to loading and perpendicular to the loading axis, on the monotonic and fatigue behavior of plain-weave fiber reinforced SiC matrix laminated composites was investigated. Two composite systems were studied: Nextel 312 (3M Corp.) reinforced SiC and Nicalon (Nippon Carbon Corp.) reinforced SiC, both fabricated by Forced Chemical Vapor Infiltration (FCVI). The behavior of both materials was investigated under monotonic and fatigue loading. Interlaminar and in-plane shear tests were conducted to further correlate shear properties with the effect of fabric orientation, with respect to the loading axis, on the orientation effects in bending. The underlying mechanisms, in monotonic and fatigue loading, were investigated through post-fracture examination using scanning electron microscopy (SEM).

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

    Energy Technology Data Exchange (ETDEWEB)

    Booker, M.K.; Majumdar, S.

    1982-01-01

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

  11. Effect of Specimen Orientation on Fatigue Crack Growth Behavior in Friction Stir Welded Al7075-T651 Joints

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yeui Han; Kim, Seon Jin [Pukyoung National University, Busan (Korea, Republic of)

    2014-12-15

    The aim of this paper is to investigate the effects of crack orientation on fatigue crack growth behavior in friction stir welded (FSWed) Al 7075-T651. Fatigue crack growth testing was conducted on compact tension (CT) specimens machined from the friction stir welds and the base metal under constant stress intensity factor range control. Tests were performed with the crack propagating nominally perpendicular to the weld line (termed the TL specimen) and the crack propagating in a parallel direction of the weld line (termed the LT specimen), and with three different constant stress intensity factor ranges. Both these specimen orientations were found to have a considerable effect on the fatigue crack growth behavior. Paris’s law was adopted for the analysis of experimental results; the exponent m of the WM-LT specimen was determined to be 3.56, which was the largest value in this experimental conditions.

  12. Effect of solution treatment on the fatigue behavior of an as-forged Mg-Zn-Y-Zr alloy

    Science.gov (United States)

    Wang, S. D.; Xu, D. K.; Wang, B. J.; Han, E. H.; Dong, C.

    2016-04-01

    Through investigating and comparing the fatigue behavior of an as-forged Mg-6.7Zn-1.3Y-0.6Zr (wt.%) alloy before and after solid solution treatment (T4) in laboratory air, the effect of T4 treatment on fatigue crack initiation was disclosed. S-N curves illustrated that the fatigue strength of as-forged samples was 110 MPa, whereas the fatigue strength of T4 samples was only 80 MPa. Observations to fracture surfaces demonstrated that for as-forged samples, fatigue crack initiation sites were covered with a layer of oxide film. However, due to the coarse grain structure and the dissolution of MgZn2 precipitates, the activation and accumulation of {10–12} twins in T4 samples were much easier, resulting in the preferential fatigue crack initiation at cracked twin boundaries (TBs). Surface characterization demonstrated that TB cracking was mainly ascribed to the incompatible plastic deformation in the twinned area and nearby α-Mg matrix.

  13. Effect of Heat Treatment on Fatigue Behavior of Biomedical Ni-Ti Alloy Wires Under Ultrasonic Conditions

    Science.gov (United States)

    Zhou, Huimin; Li, Li; Zheng, Yufeng; Li, Qingfen

    2011-06-01

    The super-elastic Ti-50.8 at.% Ni alloy wires were tested under ultrasonic conditions using a self-designed ultrasonic fatigue tester. Different heat treatment processes were subjected to Ni-Ti wires in order to obtain different combinations of phase microstructure and corresponding mechanical properties. The fatigue behavior was evaluated under ultrasonic conditions. Experimental results show that proper thermo-mechanical treatment process increased the fatigue life of Ni-Ti wire obviously, because it could adjust the microstructure of Ni-Ti alloys, as well as the work-hardening effect. The longest fatigue life of Ni-Ti wire under ultrasonic conditions was obtained when it was annealed after cold drawing. The strengthen effect of heat treatment was attributed to the fine Ti3Ni4 precipitated phase, and the strengthen effect of cold drawing was attributed to the high density of dislocations. The SEM results show that smooth fractured faces with dimples existing in the propagation region of the fatigue cracks, indicating the excellent ductility and the resistance to the propagation of fatigue cracks of NiTi wires.

  14. Microstructure and Contact Fatigue Behavior of Nano-SiO2/Ni Coating Prepared by Electro-Brush Plating

    Institute of Scientific and Technical Information of China (English)

    蒋斌; 徐滨士; 丁培道

    2003-01-01

    The composite coating nano-SiO2/Ni was prepared by co-depositing nano-SiO2 particles with pure nickel through electro-brush plating. By taking into account the effect of microstructure, heat-treatment and load on the contact fatigue life, the anti-contact fatigue behavior of the composite coating was examined and compared with that of nickel coating. As a result, the contact fatigue life decreased with the increasing of load. The contact fatigue lives of nano-SiO2/Ni coating were 16.5% and 45.2% higher than those of nickel coating respectively under the loads of 60 N and 140 N, and 326.3% higher than its counterpart of nickel coating after annealed under the load of 140 N. From the SEM image of fatigue fracture, it has been observed that the fatigue fracture of the composite coating initiated in the sub-surface as well as at the track surface due to the huddling of units, and propagated along the interface between grain units.

  15. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    Energy Technology Data Exchange (ETDEWEB)

    Sarkar, Apu, E-mail: asarkar@barc.gov.in; Kumawat, Bhupendra K.; Chakravartty, J.K.

    2015-07-15

    The cyclic stress–strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain–stress relationships and the strain–life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis.

  16. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    Science.gov (United States)

    Sarkar, Apu; Kumawat, Bhupendra K.; Chakravartty, J. K.

    2015-07-01

    The cyclic stress-strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain-stress relationships and the strain-life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis.

  17. Investigation of low-cycle fatigue behavior of austenitic stainless steel for cold-stretched pressure vessels

    Institute of Scientific and Technical Information of China (English)

    Cun-jian MIAO; Jin-yang ZHENG; Xiao-zhe GAO; Ze HUANG; A-bin GUO; Du-yi YE; Li MA

    2013-01-01

    Cold-stretched pressure vessels from austenitic stainless steels (ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301 (equivalents include UNS S30400 and AISI 304) in solution-annealed (SA) and cold-stretched conditions (9% strain level) and the response of fatigue properties to cold stretching (CS),low-cycle fatigue (LCF) tests were performed at room temperature,with total strain amplitudes ranging from ±0.4% to ±0.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1 x l03 to 2×104 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels.

  18. Mechanical Behavior and Fatigue Studies of Rubber Components Used in Tracked Vehicles

    Science.gov (United States)

    2010-08-17

    relaxation as the cycles evolve. Fatigue Modeling A MultiStage Fatigue (MSF) model developed in [3] has been applied to many types of aluminum ...McDowell, K. Gall, M.F. Horstemeyer and J. Fan. “Microstructure-based Fatigue Modeling of Cast A356 - T6 Alloy.” Engineering Fracture Mechanics, vol. 70

  19. Fatigue behavior of two alloys for Space Shuttle applications. [Inconel 903 and 718 for main engine

    Science.gov (United States)

    Adsit, N. R.; Block, S. J.

    1978-01-01

    Two superalloys used extensively in the Space Shuttle main engine are Incoloy 903 and Inconel 718. The fatigue behavior of the two alloys under varying conditions is considered. Three heats of Incoloy 903 and two of Inconel 718 were used in the study. Material was tested in several conditions, including mill polish, longitudinal mill polish, transverse mill polish, chemically milled, chemically milled plus shotpeened on one side and on both sides, gas tungsten arc welded, and electron beam welded. Both round and flat tensile specimens were tested in universal test machines. It was found that surface condition influences test results. Transverse scratches resulting from polishing and rougher surfaces lower the stress at runout in relation to that obtained on longitudinally polished and/or smooth-surfaced specimens.

  20. Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

    Institute of Scientific and Technical Information of China (English)

    J Nemati; GH Majzoobi; S Sulaiman; BTHT Baharudin; MAAzmah Hanim

    2014-01-01

    In this study, annealed pure copper was extruded using equal channel angular extrusion (ECAE) for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life con-tinued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses (or high-cycle fatigue), a maximum increase in fatigue resistance of approximately 500%was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000%was obtained for high-applied stresses (or low-cycle fatigue). Optical microscopic examinations revealed grain refinements in the range of 32 to 4 µm. A maximum increase in impact energy absorption of 100%was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the ex-truded material during fatigue tests.

  1. Study on Fatigue Behavior of Anchorage of Cable and Girder of Long Span Cable-Stayed Bridge

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A full scale model test is done and a FEM model is established toinvestigate the fatigue behavior of the Nancha cable-stayed bridge of the Nanjing Second Yangtz River Bridge, a long span steel bridge with a main span of 628 m. The results of test and FEM are analyzed and compared. It is shown that they are in good agreement. It is verified that the fatigue characteristic of the anchorage structure of cable and girder of the bridge satisfies the requirements specified by Chinese, British and American codes.

  2. High-voltage electron-microscopic observation of cyclic slip behavior around a fatigue crack tip in an iron alloy

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Yoshimasa [National Institute of Advanced Industrial Science and Technology (AIST), 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)], E-mail: yoshim.takahashi@aist.go.jp; Tanaka, Masaki; Higashida, Kenji [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Noguchi, Hiroshi [Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)

    2009-04-15

    The cyclic slip behavior around a fatigue crack tip originally located inside a bulk Fe-Si alloy was successfully observed by a high-voltage electron microscope in combination with a novel specimen preparation method. The method, by taking advantages of ion milling and focused ion beam techniques, ensures that the original shape of the crack tip is preserved without introducing additional slips. The observation confirms that the slip bands emitted from the fatigue crack tip are bounded by a labyrinth-like wall structure.

  3. Influence of Different Surface Treatments of H13 Hot Work Die Steel on Its Thermal Fatigue Behaviors

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Thermal fatigue checking is the general failure of hot work die steels, which is relative with the structures and properties of the steels and the stress alternated during the employment. The Uddeholm test method on thermal fatigue is used to compare the behaviors of different samples, which are treated with plasma nitriding、plasma sulfur-carbon-nitriding、 boronizing or not treated. The results show that the nitriding improves the thermal fatigue property of the tool steel, while the plasma sulfur-carbon-nitriding and the boronizing impair the property. The mechanisms are induced as follows. By increasing the hardness and changing the stress distribution in the surface layer, surface treatment can decrease the plastic deformation and the tensile stress during the cycling. Therefore,the generation and growth of the cracks are restrained. On the other hand, as results of surface treating, in the surface layer the toughness declines and the expanding coefficient ascendes; the latter change caused the strengthening of the tensile and compressive stress during the cycling. Thus the resistance to thermal fatigue is weakened. Whether or not the surface treatment is favor to thermal fatigue of tool steels relies on which factor is dominant.

  4. Microstructure and Fatigue Behavior of Friction Stir-welded Noncombustive Mg-9Al-Zn-Ca Magnesium Alloy

    Science.gov (United States)

    Zhou, L.; Li, Z. Y.; Nakata, K.; Feng, J. C.; Huang, Y. X.; Liao, J. S.

    2016-06-01

    Microstructure and fatigue behavior of friction stir-welded noncombustive Mg-9Al-Zn-Ca magnesium alloy were investigated. The as-received hot-extruded material consisted of equiaxed α-Mg grains with β-Mg17Al12 and Al2Ca compounds distributed along the grain boundaries. Friction stir welding produced much refined α-Mg grains accompanied by the dissolution of the eutectic β-Mg17Al12 phase, while Al2Ca phase was dispersed homogenously into the Mg matrix. Friction stir welding produced slightly increased hardness and tensile strength in the defect-free welds compared with the base material due to microstructural refinement and uniform distribution of intermetallic compounds. The load-controlled uniaxial tensile high-cycle fatigue tests indicated that fatigue strength of 90 MPa was obtained for the friction stir-welded joint with fatigue crack initiated basically near the specimen's surface and at the retreating side of the joint. Crack propagation was characterized by cleavage and fatigue striations.

  5. The effect of manufacturing conditions on discontinuity population and fatigue fracture behavior in carbon/epoxy composites

    Science.gov (United States)

    Hakim, Issa; Laquai, Rene; Walter, David; Mueller, Bernd; Graja, Paul; Meyendorf, Norbert; Donaldson, Steven

    2017-02-01

    Carbon fiber composites have been increasingly used in aerospace, military, sports, automotive and other fields due to their excellent properties, including high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and low thermal expansion coefficient. Interlaminar fracture is a serious failure mode leading to a loss in composite stiffness and strength. Discontinuities formed during manufacturing process degrade the fatigue life and interlaminar fracture resistance of the composite. In his study, three approaches were implemented and their results were correlated to quantify discontinuities effecting static and fatigue interlaminar fracture behavior of carbon fiber composites. Samples were fabricated by hand layup vacuum bagging manufacturing process under three different vacuum levels, indicated High (-686 mmHg), Moderate (-330 mmHg) and Poor (0 mmHg). Discontinuity content was quantified through-thickness by destructive and nondestructive techniques. Eight different NDE methods were conducted including imaging NDE methods: X-Ray laminography, ultrasonic, high frequency eddy current, pulse thermography, pulse phase thermography and lock-in-thermography, and averaging NDE techniques: X-Ray refraction and thermal conductivity measurements. Samples were subsequently destructively serial sectioned through-thickness into several layers. Both static and fatigue interlaminar fracture behavior under Mode I were conducted. The results of several imaging NDE methods revealed the trend in percentages of discontinuity. However, the results of averaging NDE methods showed a clear correlation since they gave specific values of discontinuity through-thickness. Serial sectioning exposed the composite's internal structure and provided a very clear idea about the type, shape, size, distribution and location of most discontinuities included. The results of mechanical testing showed that discontinuities lead to a decrease in Mode I static interlaminar

  6. Effect of heat treatment on tensile and fatigue deformation behavior of extruded Al-12 wt%Si alloy

    Science.gov (United States)

    Ham, Gi-Su; Baek, Min-Seok; Kim, Jong-Ho; Lee, Si-Woo; Lee, Kee-Ahn

    2017-01-01

    This study investigated the effect of heat treatment on tensile and high-cycle fatigue deformation behavior of extruded Al-12 wt%Si alloy. The material used in this study was extruded at a ratio of 17.7: 1 through extrusion process. To identify the effects of heat treatment, T6 heat treatment (515 °C/1 h, water quenching, and then 175 °C/10 h) was performed. Microstructural observation identified Si phases aligned in the extrusion direction in both extruded alloy (F) and heat treated alloy (T6). The average grain size of F alloy was 8.15 °C, and that of T6 alloy was 8.22 °C. Both alloys were composed of Al matrix, Si, Al2Cu, Al3Ni and AlFeSi phases. As T6 heat treatment was applied, Al2Cu phases became more finely and evenly distributed. Tensile results confirmed that yield strength increased from 119.0 MPa to 329.0 MPa, ultimate tensile strength increased from 226.8 MPa to 391.4 MPa, and the elongation decreased from 16.1% to 5.0% as T6 heat treatment was applied. High-cycle fatigue results represented F alloy's fatigue limit as 185 MPa and T6 alloy's fatigue limit as 275 MPa, indicating that high-cycle fatigue properties increased significantly as heat treatment was conducted. Through tensile and fatigue fracture surface analysis, this study considered the deformation behaviors of extruded and heat treated Al-Si alloys in relation to their microstructures.

  7. Effects of surface morphology on fatigue behavior of reduced activation ferritic/martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, S.W. [Graduate School of Energy Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)]. E-mail: kimsw@iae_kyoto-u.ac.jp; Tanigawa, H. [Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai-Mura, Ibaraki-ken 319-1195 (Japan); Hirose, T. [Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai-Mura, Ibaraki-ken 319-1195 (Japan); Shiba, K. [Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai-Mura, Ibaraki-ken 319-1195 (Japan); Kohyama, A. [Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)

    2007-08-01

    Depending on the pulse lengths, the operating conditions, and the thermal conductivity, oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep-)fatigue in the structural first wall and blanket components of fusion systems. In order to perform an accurate fatigue lifetime assessment for the international thermonuclear experimental reactor-test blanket module (ITER-TBM) and advanced systems utilizing the existing data base, mechanical understanding of fatigue fracture is mandatory. In this work, the low cycle fatigue (LCF) properties of F82H IEA heat were examined for three kinds of surface morphology with miniaturized hourglass-type fatigue specimens (SF-1). The assumed fatigue lifetime of cooling channels for ITER-TBM was also compared and assessed by correlating the results of LCF tests performed with SF-1 type specimens. Fracture surfaces and crack initiation sites were investigated by scanning electron microscopy (SEM)

  8. Fatigue crack growth behaviors of a new burn-resistant highly-stabilized beta titanium alloy

    Institute of Scientific and Technical Information of China (English)

    WU Huan; ZHAO Yongqing; ZENG Weidong; QIAN Li

    2009-01-01

    This article presents the fatigue crack growth (FCG) behaviors of a new burn-resistant highly-stabilized beta Ti40 alloy. The FCG rotes were analyzed. The fracture surfaces and the side surfaces of the test samples were explored. The results show that frequency affects the cracking behaviors of Ti40 alloy. Temperature also plays an important role in Ti40 alloy cracking. At room temperature (25℃), when the frequency increases, the cracking rate changes a little in the range of low stress intensity factor (ΔK), while it changes significantly when ΔK is high. At 500℃, the cracking rate of Ti40 alloy changes significantly during all the course of clacking. The frequency also affects the microstructure patterns of Ti40 alloy. A number of secondary cracks appear in the area more than 200 μm from the main crack at a high ΔK when the fre-quency is 1 Hz, but only a few secondary cracks exist when the frequency is 10 Hz. Facet image is the main image of the fracture surfaces when the frequency is 1 Hz. While, ductile striation occupies most of the area of fracture surfaces when the frequency is 10 Hz.

  9. Failure Behavior of Thermal Barrier Coatings on Cylindrical Superalloy Tube Under Thermomechanical Fatigue

    Institute of Scientific and Technical Information of China (English)

    Zhubing CHEN; Zhongguang WANG; Shijie ZHU

    2013-01-01

    Failure behavior of thermal barrier coatings on cylindrical superalloy tube was investigated under thermomechanical fatigue (TMF).Two types of TMF tests,i.e.in phase (IP) and out of phase (OP),were performed in the temperature range of 450-850 ℃.All tests were carried out under mechanical strain control at a given period of 300 s.The bond coat NiCrA1Y was produced by high velocity oxygen fuel (HVOF),and the top coat 7%Y2O3-ZrO2 was deposited by air plasma spraying (APS).The testing results showed that the OP TMF life was longer than the IP TMF one under the same mechanical strain amplitude.Observations of the fractured specimens revealed that the interface damage and cracking behavior in the two phasing conditions were different.In OP loading,the top coat was cracked and detached from the bond coat while no spallation was found in the IP loading.

  10. Mechanisms for Polarization Fatigue Behaviors of Perovskite Oxide Ferroelectric Thin Films

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Up to date our understanding of ferroelectric fatigue remains controversial although a huge number of experimental and theoretical approaches have been performed. The three major origins for ferroelectric fatigue are (1) charge aggregation on the ferroelectric/electrode interfaces; (2) the long-range charge transport; (3) charge-induced pinning and depinning of domains. These origins are intrinsic and they are significantly temperature-dependent. A temperature-dependent investigation of ferroelectric fatigu...

  11. Importance of the Roughness and Residual Stresses of Dental Implants on Fatigue and Osseointegration Behavior. In Vivo Study in Rabbits.

    Science.gov (United States)

    Velasco, Eugenio; Monsalve-Guil, Loreto; Jimenez, Alvaro; Ortiz, Iván; Moreno-Muñoz, Jesús; Nuñez-Marquez, Enrique; Pegueroles, Marta; Pérez, Román A; Gil, Francisco Javier

    2016-12-01

    This study focuses on the fatigue behavior and bone-implant attachment for the more usual surfaces of the different CP-titanium dental implants. The implants studied were: as-received (CTR), acid etching (AE), spark-anodization (SA), and with a grit-blasted surface (GB). Residual stresses were determined by means of X-ray diffraction. The fatigue tests were carried out at 37°C on 160 dental implants, and the stress-failure (S-N) curve was determined. The fatigue tests showed that the grit-blasting process improved fatigue life. This is a consequence of the layer of compressive residual stresses that the treatment generates in titanium surfaces. Further, our aim was to assess and compare the short- and midterm bone regenerative potential and mechanical retention of the implants in bone of New Zealand rabbits. The mechanical retention after 4 and 10 weeks of implantation was evaluated with histometric and pull-out tests, respectively, as a measure of the osseointegration of the implants. The results demonstrated that the GB treatment produced microrough that accelerated bone tissue regeneration and increased mechanical retention in the bone bed at short periods of implantation in comparison with all other implants tested. The GB surface produced an improvement in mechanical long-time behavior and improved bone growth. These types of treated implants can have great potential in clinical applications, as evidenced by the outcomes of the current study.

  12. The Effect of Elevated Temperature on the Fretting Fatigue Behavior of Nickel Alloy IN-100

    Science.gov (United States)

    2008-04-01

    Saladin S-N data points for plain fatigue 86 4.16 Comparison of Ownby and Saladin S-N data points for fretting fatigue 87 4.17 Comparison of Ownby...and Saladin S-N data for all tests 88 4.18 Plot comparing ΔQ vs Nf from Ownby, Saladin & Madhi data points 89 4.19 Plot from Kawagoishi et al. [21...in this study 93 4.3 Madhi fretting and plain fatigue testing data 94 4.4 Saladin fretting and plain fatigue testing data 94 4.5 Comparison of

  13. Fatigue in adolescents and young adults with sickle cell disease: biological and behavioral correlates and health-related quality of life.

    Science.gov (United States)

    Ameringer, Suzanne; Elswick, R K; Smith, Wally

    2014-01-01

    This descriptive, correlational study examined fatigue and potential biological and behavioral correlates in adolescents and young adults with sickle cell disease. Sixty adolescents and young adults with sickle cell disease completed the Brief Fatigue Inventory, Multidimensional Fatigue Symptom Inventory-Short Form, Patient Reported Outcomes Measurement Information System (PROMIS) fatigue short form and measures of pain, sleep quality, anxiety, depressive mood, stress, disease severity, and quality of life. Blood samples were obtained for hemoglobin and cytokines. Fatigue scores were mostly moderate in severity. Fatigue interfered to a moderate degree with daily activities and correlated significantly with pain, sleep quality, state and trait anxiety, depressive mood, stress, and quality of life. Fatigue was correlated with hemoglobin on the PROMIS measure. Fatigue was not correlated with cytokines or age, nor differed by disease severity. Fatigue was common in these adolescents and young adults, interfered with daily activities such as school, work and exercise, and significantly correlated with several potentially modifiable factors. As life expectancy increases in sickle cell disease, research is needed to test interventions to reduce fatigue.

  14. Tension-Tension Fatigue Behavior of Unidirectional C/Sic Ceramic-Matrix Composite at Room Temperature and 800 °C in Air Atmosphere

    Directory of Open Access Journals (Sweden)

    Longbiao Li

    2015-06-01

    Full Text Available The tension-tension fatigue behavior of unidirectional C/SiC ceramic-matrix composite at room temperature and 800 °C under air has been investigated. The fatigue hysteresis modulus and fatigue hysteresis loss energy corresponding to different number of applied cycles have been analyzed. The fatigue hysteresis loops models for different interface slip cases have been derived based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading. The fiber/matrix interface shear stress has been estimated for different numbers of applied cycles. By combining the interface shear stress degradation model and fibers strength degradation model with fibers failure model, the tension-tension fatigue life S-N curves of unidirectional C/SiC composite at room temperature and 800 °C under air have been predicted.

  15. Fatigue in Rheumatoid Arthritis.

    Science.gov (United States)

    Katz, Patricia

    2017-05-01

    The purpose of this study was to review the current information on fatigue in rheumatoid arthritis (RA). Severe fatigue is common among individuals with RA and has a significant impact on quality of life (QOL). RA-related factors (e.g., inflammation, pain) are associated with greater fatigue, but other factors, such as obesity, physical inactivity, sleep disturbance, and depression, explain the majority of variation in fatigue. Medications targeting RA have little effect on fatigue. Instead, the most effective interventions seem to address non-RA-specific factors such as physical inactivity or use cognitive behavioral approaches. No recommendations have been made for tools to measure fatigue in RA, leading to potential difficulty comparing studies. Although fatigue has great impact on patients' QOL, effective interventions that are feasible for broad dissemination remain elusive. Additional multi-faceted research is needed to identify modifiable sources of fatigue. Such research would be enhanced by harmonization of fatigue measurement across studies.

  16. Chronic post-inflammatory fatigue in sarcoidosis : from cytokines to behavior

    NARCIS (Netherlands)

    Korenromp, I.H.E.

    2011-01-01

    Sarcoidosis is a systemic inflammatory disorder that is characterized by granuloma formation in different organs. Sarcoidosis patients frequently report fatigue. Even when the clinical symptoms of the inflammatory disease sarcoidosis have resolved, chronic fatigue may persist. In this study 75 patie

  17. Fatigue behaviors and damage mechanism of a Cr-Mn-N austenitic steel

    DEFF Research Database (Denmark)

    Lv, Z.; Cai, P.; Yu, Tianbo;

    2017-01-01

    Four-point bending fatigue tests were conducted on a Cr-Mn-N austenitic steel at room temperature, at frequency of 20 Hz and the stress ratio of R = 0.1, in air. The fatigue strength of this Cr-Mn-N austenitic steel was measured to be 503 MPa in the maximum stress from the S-N curve obtained...

  18. Multiaxial fatigue behavior of conventional and highly crosslinked UHMWPE during cyclic small punch testing.

    Science.gov (United States)

    Villarraga, M L; Kurtz, S M; Herr, M P; Edidin, A A

    2003-08-01

    Previous observations of reduced uniaxial elongation, fracture resistance, and crack propagation resistance of highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) have contributed to concern that the technology may not be appropriate for systems undergoing cyclic fatigue loading. Using a "total life" approach, we examined the influence of radiation crosslinking on the fatigue response of UHMWPE under cyclic loading via the small punch test. Our goal in this study was to evaluate the suitability of the small punch test for conducting miniature-specimen, cyclic loading, and fatigue experiments of conventional and highly crosslinked UHMWPE. We subjected four types of conventional and highly crosslinked UHMWPE to cyclic loading at 200 N/s and at body temperature in a small punch test apparatus. After failure, the fracture surfaces were characterized with the use of field emission scanning electron microscopy to evaluate the fatigue mechanisms. Cyclic small punch testing under load control was found to be an effective and repeatable method for relative assessment of the fatigue resistance of conventional and highly crosslinked UHMWPE specimens under multiaxial loading conditions. For each of the four conventional and highly crosslinked UHMWPE materials evaluated in this study, fatigue failures were consistently produced according to a power law relationship in the low cycle regimen, corresponding to failures below 10000 cycles. The fatigue failures were all found to be consistent with a single source of initiation and propagation to failure. Our long-term goal in this research is to develop miniature-specimen fatigue testing techniques for characterization of retrieved UHMWPE inserts.

  19. Effect of Cryorolling and Aging on Fatigue Behavior of Ultrafine-grained Al6061

    Science.gov (United States)

    Yadollahpour, M.; Hosseini-Toudeshky, H.; Karimzadeh, F.

    2016-05-01

    The effects of cryorolling (rolling at liquid nitrogen temperature) and heat treatment on tensile and high-cycle fatigue properties and fatigue crack growth rate of Al6061 alloy have been investigated in the present work. First, the solid solution-treated bulk Al6061 alloy was subjected to cryorolling with 90% total thickness reduction and subsequent short annealing at 205°C for 5 min and peak aging at 148°C for 39 h to achieve grain refinement and simultaneous improvement of the strength and ductility. Then, hardness measurements, tensile tests, fatigue life, and fatigue crack growth rate tests including fractography analyses using scanning electron microscopy were performed on bulk Al6061 alloy, cryorolled (CR), and cryorolled material followed by peak aging (PA). The PA specimen showed improved yield strength by 24%, ultimate tensile strength by 20%, and ductility by 12% as compared with the bulk Al6061 alloy. It is shown that the fatigue strength of both CR and PA specimens under a high-cycle fatigue regime are larger than that of the bulk Al6061 alloy. Also, fatigue crack growth rates of the CR and PA specimens show significant enhancement in fatigue crack growth resistances as compared with the bulk Al6061 alloy, as a result of grain refinement.

  20. How Thermal Fatigue Cycles Change the Rheological Behavior of Polymer Modified Bitumen?

    NARCIS (Netherlands)

    Glaoui, B.; Merbouh, M.; Van de Ven, M.F.C.; Chailleux, E.; Youcefi, A.

    2013-01-01

    The paper deals with the problem of thermal fatigue cycles phenomenon, which affects the performance of flexible pavement. The purpose of the paper is to extent the knowledge on the rheology of polymer modified bitumen which was affected by cycles of thermal fatigue. The aim of this research is to d

  1. Fatigue behaviors of Z2CND18.12N stainless steel under thermal-mechanical cycling

    Institute of Scientific and Technical Information of China (English)

    Liubing WANG; Dunji YU; Fei XUE; Weiwei YU; Jian CHEN; Xu CHEN

    2011-01-01

    Tests under mechanical strain control were performed to investigate the TMF behavior of Z2CND18.12N within the temperature range between 150-550 ℃. Differentstrain amplitudes and phase-angles were applied. Total strain controlled low cycle fatigue test was also performed at the peak temperature of TMF cycling. The results show that the cyclic stress response of the material displayed an initial hardening regime followed by a saturation period and then cyclic softening till failure. The TMF cycling leads to the development of significant amounts of mean stress. Some life prediction models were employed to predict the TMF life of Z2CND18.12N, and the results indicate that the energy-based models provide good prediction on the thermal-mechanical fatigue behaviors of this material. An optical microscopic observation shows that the surface crack initiations and crack propagations are typicallytransgranular mode.

  2. Flex Fatigue Behavior Of Plastic Optical Fibers With Low Bending Cycles

    Directory of Open Access Journals (Sweden)

    Huang Juan

    2015-06-01

    Full Text Available Flex fatigue behaviour of plastic optical fibres (POFs with the diameters of 0.2 and 0.3 mm under different pretensions is measured with fatigue life curve by flexometer. The fatigue sensitivity coefficient is calculated by the linear fitting curve of normalised stress versus logarithm of bending cycles. The residual modulus is investigated during the flex fatigue processes. The results exhibit the exponential relationship between applied pretension and numbers of bending cycles at break. It is indicated that the flex fatigue of POFs might be sensitive with high swing angle or swing speed. There is an evident loss of modulus for two POFs with pretensions of 4 and 10% of ultimate tensile strength during 10-times bending cycles. The values of residual modulus of two POFs almost keep constant after 10-times bending cycles.

  3. Influence of PbBi environment on the low-cycle fatigue behavior of SNS target container materials

    Energy Technology Data Exchange (ETDEWEB)

    Kalkhof, D.; Grosse, M. E-mail: micro.grosse@psi.ch

    2003-05-15

    The low-cycle fatigue (LCF) behavior of the stainless steel 316L and the 10.5Cr-steel Manet-II was investigated at 260 deg. C in air and in stagnant lead-bismuth (PbBi). At low-strain levels, the fatigue lives for 316L in PbBi and air were comparable. At total strain amplitudes of 0.50% and higher a weak influence of PbBi was observed. In contrast to 316L, the results of LCF tests for Manet-II in PbBi showed a significant reduction of lifetime for all applied strain amplitudes. In the worst case the cycle number to crack initiation was reduced by a factor of {approx}7 compared with the comparable test in air. For the low-strain amplitude of 0.30%, fatigue tests conducted at a frequency of 0.1 Hz had shorter fatigue lives than at a frequency of 1.0 Hz. For Manet-II the crack propagation in PbBi was much faster than in air, and failure immediate followed the formation of the first macroscopic crack.

  4. Fatigue Behavior of Ultrafine-Grained Medium Carbon Steel with Different Carbide Morphologies Processed by High Pressure Torsion

    Directory of Open Access Journals (Sweden)

    Christoph Ruffing

    2015-05-01

    Full Text Available The increased attention ultrafine grained (UFG materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT.

  5. Effect of Stress Ratio and Loading Frequency on the Corrosion Fatigue Behavior of Smooth Steel Wire in Different Solutions

    Directory of Open Access Journals (Sweden)

    Songquan Wang

    2016-09-01

    Full Text Available In this work, the effects of loading condition and corrosion solution on the corrosion fatigue behavior of smooth steel wire were discussed. The results of polarization curves and weight loss curves showed that the corrosion of steel wire in acid solution was more severe than that in neutral and alkaline solutions. With the extension of immersion time in acid solution, the cathodic reaction of steel wire gradually changed from the reduction of hydrogen ion to the reduction of oxygen, but was always the reduction of hydrogen ion in neutral and alkaline solutions. The corrosion kinetic parameters and equivalent circuits of steel wires were also obtained by simulating the Nyquist diagrams. In corrosion fatigue test, the effect of stress ratio and loading frequency on the crack initiation mechanism was emphasized. The strong corrosivity of acid solution could accelerate the nucleation of crack tip. The initiation mechanism of crack under different conditions was summarized according to the side and fracture surface morphologies. For the crack initiation mechanism of anodic dissolution, the stronger the corrosivity of solution was, the more easily the fatigue crack source formed, while, for the crack initiation mechanism of deformation activation, the lower stress ratio and higher frequency would accelerate the generation of corrosion fatigue crack source.

  6. Effects of Strain Ratio on Fatigue Behavior of G20Mn5QT Cast Steel

    Institute of Scientific and Technical Information of China (English)

    韩庆华; 郭琪; 尹越; 邢颖

    2016-01-01

    Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be em-ployed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropri-ate ranges ofS-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.

  7. Fatigue crack growth behavior of the simulated HAZ of 800 MPa grade high-performance steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sanghoon [Division of Materials Science and Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Kang, Donghwan; Kim, Tae-Won [School of Mechanical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Lee, Jongkwan [Research Institute of Industrial Science and Technology, 75-9, Youngcheon, Dongtan, Hwaseong, Gyeonggi-do 445-813 (Korea, Republic of); Lee, Changhee, E-mail: chlee@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

    2011-03-15

    Research highlights: {yields} Fatigue crack resistances of HSB800 base steel and HAZs: Base steel > FGHAZ > CGHAZ > ICCGHAZ. {yields} In the case of ICCGHAZ, fatigue cracks are rapidly initiated and propagated through massive M-A constituents. {yields} Fatigue crack growth rate of CGHAZ was faster than that of FGHAZ, mainly due to the coarsened prior austenite grain and martensite packet. - Abstract: The present study focuses on the fatigue properties in the weld heat-affected zone (HAZ) of 800 MPa grade high-performance steel, which is commonly used in bridges and buildings. Single- and multi-pass HAZs were simulated by the Gleeble system. Fatigue properties were estimated using a crack propagation test under a 0.3 stress ratio and 0.1 load frequencies. The microstructures and fracture surfaces were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results of the crack propagation test showed that the fatigue crack growth rate of coarse-grained HAZ (CGHAZ) was faster than fine-grained HAZ (FGHAZ), although both regions have identical fully martensite microstructures, because FGHAZ has smaller prior austenite grain and martensite packet sizes, which can act as effective barriers to crack propagation. The fatigue crack growth rate of intercritically reheated CGHAZ (ICCGHAZ) was the fastest among local zones in the HAZ, due to rapid crack initiation and propagation via the massive martensite-austenite (M-A) constituent.

  8. Effect of microstructure on fatigue behavior of advanced high strength steels produced by quenching and partitioning and the role of retained austenite

    Energy Technology Data Exchange (ETDEWEB)

    Diego-Calderón, I. de, E-mail: irenedediego.calderon@imdea.org [IMDEA Materials Institute, Calle Eric Kandel 2, 28906 Getafe, Madrid (Spain); Rodriguez-Calvillo, P. [Fundació CTM Centre Tecnològic, Plaza de la Ciencia 2, 08243 Manresa (Spain); Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona (Spain); Lara, A. [Fundació CTM Centre Tecnològic, Plaza de la Ciencia 2, 08243 Manresa (Spain); Molina-Aldareguia, J.M. [IMDEA Materials Institute, Calle Eric Kandel 2, 28906 Getafe, Madrid (Spain); Petrov, R.H. [Department of Materials Science and Engineering, Ghent University, Technologiepark 903, B-9052 Zwijnaarde (Ghent) (Belgium); Department of Materials Science and Engineering, Delft University of Technology, 2628 CD Delft (Netherlands); De Knijf, D. [Department of Materials Science and Engineering, Ghent University, Technologiepark 903, B-9052 Zwijnaarde (Ghent) (Belgium); Sabirov, I. [IMDEA Materials Institute, Calle Eric Kandel 2, 28906 Getafe, Madrid (Spain)

    2015-08-12

    Despite the significant body of research on mechanical properties of quenched and partitioned (Q&P) steels, their fatigue behavior has not been investigated. This work focuses on the effect of microstructure on high cycle fatigue of Q&P steels and microstructural evolution during cyclic loading. It is demonstrated that increased content of retained austenite (RA) improves fatigue limit of Q&P steels that is related to delay of crack propagation due to austenite–martensite phase transformation. Increasing stress amplitude promotes austenite–martensite phase transformation during cycling loading. It is shown that size and crystallographic orientation of RA are the main factors determining its stability, whereas its shape and spatial distribution do not seem to affect it significantly. Fatigue crack initiation during fatigue testing with high stress amplitudes occurs by intergranular cracking, whereas transgranular cracking controls fatigue crack initiation during cycling loading with lower stress amplitudes. Transgranular crack propagation dominates in the second stage of fatigue at all stress amplitudes. The final stage of fatigue is also not affected by the stress amplitude. It is suggested that fatigue life of Q&P steels can be enhanced via improvement of strength of grain/interphase boundaries.

  9. Fatigue behavior in austenitic stainless steels in high-temperature water

    Science.gov (United States)

    Smith, Jean Laverty

    The fatigue life of Type 304 and Type 316NG austenitic stainless steel has been shown to be significantly lower in light water reactor environments than in air at 288°C. The focus of this study was to determine the effect of dissolved oxygen (DO) on fatigue crack initiation and early crack growth at 288°C using fully-reversed, constant strain, axial fatigue tests. The fatigue tests were chosen to evaluate fracture surface appearance, fatigue crack lengths, and fatigue crack growth rates. Additional studies were conducted to evaluate the oxide film growth kinetics of Type 304 and Type 316NG stainless steel in high-temperature water. Corrosion coupons were exposed for intervals up to 50 days to high-temperature water at 288°C with two different levels of dissolved oxygen. The coupons were evaluated for weight change, oxide film thickness, and oxide film composition. The fatigue testing and oxide evaluations conducted in this study indicate that in low-DO water, the bulk environment does not allow a passive film to form, and newly created metal surfaces do not oxidize. Fatigue cracks propagate as Mode I tensile cracks normal to the stress axis from the onset. The apparent lack of Stage I crack growth in low-DO water accounts for the significant reduction in life in this environment as compared to air. In high-DO water, the bulk environment supports the formation of a passive film and prevents the evolution of hydrogen. Crack growth initially occurs only along primary slip planes at angles 45° to the applied stress. As the crack length increases, the crack tip environment becomes increasingly independent of the bulk environment, water at the crack tip becomes unstable, and the newly created surfaces no longer re-oxidize. Subsequently, the increasing stress intensity allows slip to occur on additional planes, and the fatigue crack propagates as a Mode I tensile crack.

  10. Fatigue Performance of Friction-Stir-Welded Al-Mg-Sc Alloy

    Science.gov (United States)

    Zhemchuzhnikova, Daria; Mironov, Sergey; Kaibyshev, Rustam

    2017-01-01

    Fatigue behavior of a friction-stir-welded Al-Mg-Sc alloy was examined in cast and hot-rolled conditions. In both cases, the joints failed in the base material region and therefore the joint efficiency was 100 pct. The specimens machined entirely from the stir zone demonstrated fatigue strength superior to that of the base material in both preprocessed tempers. It was shown that the excellent fatigue performance of friction-stir joints was attributable to the ultra-fine-grained microstructure, the low dislocation density evolved in the stir zone, and the preservation of Al3Sc coherent dispersoids during welding. The formation of such structure hinders the initiation and growth of fatigue microcracks that provides superior fatigue performance of friction-stir welds.

  11. Local fatigue behavior in tapered areas of large offshore wind turbine blades

    DEFF Research Database (Denmark)

    Raeis Hosseiny, Seyed Aydin; Jakobsen, Johnny

    2016-01-01

    failure of an entire blade structure. The local strength degradation under an ultimate static loading, subsequent to several years of fatigue, is predicted for an offshore wind turbine blade. Fatigue failure indexes of different damage modes are calculated using a sub-modeling approach. Multi axial...... stresses are accounted for using a developed failure criterion with residual strengths instead of the virgin strengths. Damage initiation is predicted by including available Wohler curve data of E-Glass fabrics and epoxy matrix into multi-axial fatigue failure criteria. As a result of this study, proper...... knock-down factors for ply-drop effects in wind turbine blades under multi-axial static and fatigue loadings can be obtained....

  12. Local fatigue behavior in tapered areas of large offshore wind turbine blades

    Science.gov (United States)

    Aydin Raeis Hosseiny, Seyed; Jakobsen, Johnny

    2016-07-01

    Thickness transitions in load carrying elements lead to improved geometries and efficient material utilization. However, these transitions may introduce localized areas with high stress concentrations and may act as crack initiators that could potentially cause delamination and further catastrophic failure of an entire blade structure. The local strength degradation under an ultimate static loading, subsequent to several years of fatigue, is predicted for an offshore wind turbine blade. Fatigue failure indexes of different damage modes are calculated using a sub-modeling approach. Multi axial stresses are accounted for using a developed failure criterion with residual strengths instead of the virgin strengths. Damage initiation is predicted by including available Wohler curve data of E-Glass fabrics and epoxy matrix into multi-axial fatigue failure criteria. As a result of this study, proper knock-down factors for ply-drop effects in wind turbine blades under multi-axial static and fatigue loadings can be obtained.

  13. Low Cycle Fatigue Behavior of HT250 Gray Cast Iron for Engine Cylinder Blocks

    Science.gov (United States)

    Fan, K. L.; He, G. Q.; She, M.; Liu, X. S.; Yang, Y.; Lu, Q.; shen, Y.; Tian, D. D.

    2014-08-01

    The strain-controlled low cycle fatigue properties were evaluated on specimens of HT250 gray cast iron (GCI) at room temperature. The material exhibited cyclic stabilization at a low strain amplitude of 0.1% and cyclic softening characteristic at higher strain amplitudes (0.15-0.30%). At a representative total strain amplitude (0.30%), the hysteresis loops of HT250 GCI were asymmetric with a large amount of plastic deformation in the compressive phases. Furthermore, the hysteresis loop became larger in both width and height with increasing total strain amplitude (from 0.10 to 0.30%), and tended to exhibit a clockwise rotation. The fatigue crack propagation mechanisms were different at various total strain amplitudes, where high stress concentration due to dislocation pile-up favored fatigue crack initiation in the examined HT250. Finally, the roughness-induced crack closure was a key to determine the crack growth rate as well as fatigue life.

  14. Effect of superplastic forming exposure on fatigue crack propagation behavior of Ti-6Al-4V alloy

    Science.gov (United States)

    Jeong, Daeho; Kwon, Yongnam; Goto, Masahiro; Kim, Sangshik

    2016-09-01

    The effect of superplastic forming (SPF) exposure on the ɛ (strain)-N (number of cycles to failure) fatigue and fatigue crack propagation (FCP) behaviors of Ti-6Al-4V (Ti64) alloy was examined at 298 and 473 K. To simulate the thermal exposure during superplastic forming process, the mill-annealed Ti64 alloy sheet was heated in the vacuum chamber with the pre-determined temperature profile. Notable microstructural change during the SPF exposure included the shape of transformed β phase from fine and round particles in the as-received specimen to coarse angular particles in the as-exposed specimen. The effective grain size tended to increase with the exposure, enhancing the slip reversibility and the resistance to FCP. However, the crack hindering effect by fine, particle-like β phase became weak with the exposure, offseting the beneficial effect associated with the increment of effective grain size. The effect of SPF exposure on ɛ-N fatigue and FCP behavior of mill-annealed Ti64 alloy was therefore marginal, excluding the effect of α-case (the oxygen-enriched phase) on the surface.

  15. Fatigue-crack growth behavior of Type 347 stainless steels under simulated PWR water conditions

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seokmin; Min, Ki-Deuk; Yoon, Ji-Hyun; Kim, Min-Chul; Lee, Bong-Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    Fatigue crack growth rate (FCGR) curve of stainless steel exists in ASME code section XI, but it is still not considering the environmental effects. The longer time nuclear power plant is operated, the more the environmental degradation issues of materials pop up. There are some researches on fatigue crack growth rate of S304 and S316, but researches of FCGR of S347 used in Korea nuclear power plant are insufficient. In this study, the FCGR of S347 stainless steel was evaluated in the PWR high temperature water conditions. The FCGRs of S347 stainless steel under pressurized-water conditions were measured by using compact-tension (CT) specimens at different levels of dissolved oxygen (DO) and frequency. 1. FCGRs of SS347 were slower than that in ASME XI and environmental effect did not occur when frequency was higher than 1Hz. 2. Fatigue crack growth is accelerated by corrosion fatigue and it is more severe when frequency is slower than 0.1Hz. 3. Increase of crack tip opening time increased corrosion fatigue and it deteriorated environmental fatigue properties.

  16. Fatigue Crack Growth Rate Behavior of Type 347 Stainless Steel in Simulated PWR Water Environment

    Energy Technology Data Exchange (ETDEWEB)

    Min, Ki Deuk; Kim, Seon Jin [Hanyang University, Seoul (Korea, Republic of); Kim, Dae Whan; Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    The pressurizer surge line of a Korean standard nuclear power plane uses Nb stabilized type 347 stainless steel. The pressurizer surge line is the pipe connecting the pressurizer and the hot leg line, and the path controlling the pressure and temperature of the cooling system of the nuclear reactor, operated at 316 .deg. C and in a 150atm. The pressurizer surge line operated at high temperature and high pressure receives thermal stress by a temperature change and mechanical stress by a pressure change at the same time, and by being exposed to the high temperature and high pressure cooling water environment of a nuclear power plant, environmental fatigue by stress and corrosion is the main damage instrument. As the effect of environmental fatigue has been reported, through low cycle fatigue, fatigue life evaluations of austenite stainless steel have been conducted, but evaluations of fatigue crack growth rate to evaluate the soundness are very poor. In this study, evaluated characteristics of fatigue crack growth rate base on a change of dissolved oxygen in a PWR environment

  17. Effects of hydrogen water chemistry on corrosion fatigue behavior of cold-worked 304L stainless steel in simulated BWR coolant environments

    Energy Technology Data Exchange (ETDEWEB)

    Chiang, M.F., E-mail: mfchiang@iner.gov.tw [Institute of Nuclear Energy Research, Division of Nuclear Fuels and Materials, Lungtan, Taoyuan 325, Taiwan (China); Young, M.C.; Huang, J.Y. [Institute of Nuclear Energy Research, Division of Nuclear Fuels and Materials, Lungtan, Taoyuan 325, Taiwan (China)

    2011-04-15

    Corrosion fatigue behavior of stainless steel 304L (SS304L) in a simulated BWR coolant with hydrogen injection was investigated. Hydrogen water chemistry slightly mitigated the corrosion fatigue degradation of the as-received SS304L specimens, but, on the contrary, it slightly increased the corrosion fatigue crack growth rates (CFCGRs) of the cold-worked specimens. All the CFCGR-tested specimens showed similar fracture features, except for the amounts of deposited corrosion debris. The results indicated that decreasing the oxygen concentration of water environment is not an effective measure to suppress the fatigue crack growth rate of cold-worked SS304L. The CFCGRs of the SS304L were determined by an interaction between corrosion, oxide-induced crack closure and cold work in corrosive environments. At a specific level of reduction, cold work could enhance the corrosion fatigue resistance of SS304 both in the air-saturated and HWC coolant environments.

  18. Effects of hydrogen water chemistry on corrosion fatigue behavior of cold-worked 304L stainless steel in simulated BWR coolant environments

    Science.gov (United States)

    Chiang, M. F.; Young, M. C.; Huang, J. Y.

    2011-04-01

    Corrosion fatigue behavior of stainless steel 304L (SS304L) in a simulated BWR coolant with hydrogen injection was investigated. Hydrogen water chemistry slightly mitigated the corrosion fatigue degradation of the as-received SS304L specimens, but, on the contrary, it slightly increased the corrosion fatigue crack growth rates (CFCGRs) of the cold-worked specimens. All the CFCGR-tested specimens showed similar fracture features, except for the amounts of deposited corrosion debris. The results indicated that decreasing the oxygen concentration of water environment is not an effective measure to suppress the fatigue crack growth rate of cold-worked SS304L. The CFCGRs of the SS304L were determined by an interaction between corrosion, oxide-induced crack closure and cold work in corrosive environments. At a specific level of reduction, cold work could enhance the corrosion fatigue resistance of SS304 both in the air-saturated and HWC coolant environments.

  19. Thermomechanical and Isothermal Fatigue Behavior of 316LN Stainless Steel with Varying Nitrogen Content

    Science.gov (United States)

    Prasad Reddy, G. V.; Nagesha, A.; Sandhya, R.; Sankaran, S.; Mathew, M. D.; Bhanu Sankara Rao, K.

    2015-02-01

    Thermomechanical (TMF) and isothermal (IF) fatigue behavior of 316LN stainless steel alloyed with 0.07, 0.14, and 0.22 wt pct nitrogen is presented in this manuscript. In the TMF tests with temperature cycling in the range of 573 K to 873 K (300 °C to 600 °C), life decreased with increasing nitrogen content for both in-phase (IP) and out-of-phase (OP) cycling, with a peak at 0.07 wt pct N. In contrast, 0.14 wt pct N yielded maximum life under IF cycling carried out at 873 K (600 °C). Cyclic lives are seen to follow the sequence, IP-TMF < IF < OP-TMF cycling, and it remained same irrespective of the nitrogen content in 316LN SS. Lives under IP-TMF are lower than those in OP cycling by a factor of 2 to 2.5, in spite of the higher cyclic stress response in OP cycling. At all the nitrogen contents in the present study, nitrogen and dynamic strain aging induced slip localization in the form of planar slip bands both in IP and OP-TMF, in comparison to IF deformation wherein complete planar slip mode of deformation is evidenced only at 0.22 wt pct N. In TMF studies, increasing nitrogen content promoted strong slip localization ( i.e., increase in slip band density with a decrease in interband spacing) in combination with high tensile cyclic stresses that marred the beneficial effect of nitrogen content on TMF life.

  20. Motor learning in individuals with autism spectrum disorder: activation in superior parietal lobule related to learning and repetitive behaviors.

    Science.gov (United States)

    Travers, Brittany G; Kana, Rajesh K; Klinger, Laura G; Klein, Christopher L; Klinger, Mark R

    2015-02-01

    Motor-linked implicit learning is the learning of a sequence of movements without conscious awareness. Although motor symptoms are frequently reported in individuals with autism spectrum disorder (ASD), recent behavioral studies have suggested that motor-linked implicit learning may be intact in ASD. The serial reaction time (SRT) task is one of the most common measures of motor-linked implicit learning. The present study used a 3T functional magnetic resonance imaging scanner to examine the behavioral and neural correlates of real-time motor sequence learning in adolescents and adults with ASD (n = 15) compared with age- and intelligence quotient-matched individuals with typical development (n = 15) during an SRT task. Behavioral results suggested less robust motor sequence learning in individuals with ASD. Group differences in brain activation suggested that individuals with ASD, relative to individuals with typical development, showed decreased activation in the right superior parietal lobule (SPL) and right precuneus (Brodmann areas 5 and 7, and extending into the intraparietal sulcus) during learning. Activation in these areas (and in areas such as the right putamen and right supramarginal gyrus) was found to be significantly related to behavioral learning in this task. Additionally, individuals with ASD who had more severe repetitive behavior/restricted interest symptoms demonstrated greater decreased activation in these regions during motor learning. In conjunction, these results suggest that the SPL may play an important role in motor learning and repetitive behavior in individuals with ASD.

  1. Inhibition drives configural superiority of illusory Gestalt: Combined behavioral and drift-diffusion model evidence.

    Science.gov (United States)

    Nie, Qi-Yang; Maurer, Mara; Müller, Hermann J; Conci, Markus

    2016-05-01

    Illusory Kanizsa figures demonstrate that a perceptually completed whole is more than the sum of its composite parts. In the current study, we explored part/whole relationships in object completion using the configural superiority effect (CSE) with illusory figures (Pomerantz & Portillo, 2011). In particular, we investigated to which extent the CSE is modulated by closure in target and distractor configurations. Our results demonstrated a typical CSE, with detection of a configural whole being more efficient than the detection of a corresponding part-level target. Moreover, the CSE was more pronounced when grouped objects were presented in distractors rather than in the target. A follow-up experiment systematically manipulated closure in whole target or, respectively, distractor configurations. The results revealed the effect of closure to be again stronger in distractor, rather than in target configurations, suggesting that closure primarily affects the inhibition of distractors, and to a lesser extent the selection of the target. In addition, a drift-diffusion model analysis of our data revealed that efficient distractor inhibition expedites the rate of evidence accumulation, with closure in distractors particularly speeding the drift toward the decision boundary. In sum, our findings demonstrate that the CSE in Kanizsa figures derives primarily from the inhibition of closed distractor objects, rather than being driven by a conspicuous target configuration. Altogether, these results support a fundamental role of inhibition in driving configural superiority effects in visual search.

  2. Effect of the welding profile generated by the modified indirect electric arc technique on the fatigue behavior of 6061-T6 aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ambriz, R.R., E-mail: ricraf74@gmail.com [Universite Lille Nord de France, F-59000 Lille (France); USTL, LML, F-59650 Villeneuve d' Ascq (France); CNRS, UMR 8107, F-59650 Villeneuve d' Ascq (France); Mesmacque, G. [Universite Lille Nord de France, F-59000 Lille (France); USTL, LML, F-59650 Villeneuve d' Ascq (France); CNRS, UMR 8107, F-59650 Villeneuve d' Ascq (France); Ruiz, A. [Instituto de Investigaciones Metalurgicas, Universidad Michoacana de San Nicolas de Hidalgo, A.P. 888, C.P. 58000, Morelia Michoacan (Mexico); Amrouche, A. [Universite Lille Nord de France, F-59000 Lille (France); USTL, LML, F-59650 Villeneuve d' Ascq (France); CNRS, UMR 8107, F-59650 Villeneuve d' Ascq (France); Lopez, V.H. [Instituto de Investigaciones Metalurgicas, Universidad Michoacana de San Nicolas de Hidalgo, A.P. 888, C.P. 58000, Morelia Michoacan (Mexico)

    2010-03-25

    This paper reports the effect of the welding profile generated by the modified indirect electric arc (MIEA) technique on the fatigue behavior of 6061-T6 welded joints. The calculations are based on the effect of the stress concentration factor produced by the characteristic geometry of the welding profile formed during the welding process. It was found that the fatigue life of welded samples using this welding technique was larger in comparison with data reported in the literature. Also, measurements of microhardness and tension testing were performed to account for the effect of different levels of fatigue damage on the mechanical properties of these welds. Experimental findings reveal that, with reference to undamaged samples, fatigue damage increases the microhardness in the weld metal and heat affected zone (HAZ) whereas it only produces a moderate increase in yield strength of approximately 14% for a 75% of fatigue damage. Tensile and fatigue tests indicate that the thermal affection undergone by the plates during fusion welding dictates failure in the HAZ under tension stress but not under fatigue. The failure mechanism under fatigue is discussed in terms of theoretical analyses and fractography.

  3. The role of left superior parietal lobe in male sexual behavior: dynamics of distinct components revealed by FMRI.

    Science.gov (United States)

    Cera, Nicoletta; Di Pierro, Ezio D; Sepede, Gianna; Gambi, Francesco; Perrucci, Mauro Gianni; Merla, Arcangelo; Tartaro, Armando; Del Gratta, Cosimo; Galatioto Paradiso, Giuseppe; Vicentini, Carlo; Romani, Gian Luca; Ferretti, Antonio

    2012-06-01

    Despite the interest for the brain correlates of male sexual arousal, few studies investigated neural mechanisms underlying psychogenic erectile dysfunction (ED). Although these studies showed several brain regions active in ED patients during visual erotic stimulation, the dynamics of inhibition of sexual response is still unclear. This study investigated the dynamics of brain regions involved in the psychogenic ED. Functional magnetic resonance imaging (fMRI) and simultaneous penile tumescence (PT) were used to study brain activity evoked in 17 outpatients with psychogenic ED and 19 healthy controls during visual erotic stimulation. Patterns of brain activation related to different phases of sexual response in the two groups were compared. Simultaneous recording of blood oxygen level-dependent fMRI responses and PT during visual erotic stimulation. During visual erotic stimuli, a larger activation was observed for the patient group in the left superior parietal lobe, ventromedial prefrontal cortex, and posterior cingulate cortex, whereas the control group showed larger activation in the right middle insula and dorsal anterior cingulate cortex and hippocampus. Moreover, the left superior parietal lobe showed a larger activation in patients than controls especially during the later stage of sexual response. Our results suggest that, among regions more active in patient group, the left superior parietal lobe plays a crucial role in inhibition of sexual response. Previous studies showed that left superior parietal lobe is involved in monitoring of internal body representation. The larger activation of this region in patients during later stages of sexual response suggests a high monitoring of the internal body representation, possibly affecting the behavioral response. These findings provide insight on brain mechanisms involved in psychogenic ED. © 2012 International Society for Sexual Medicine.

  4. The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Wenke Li

    2016-09-01

    Full Text Available Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that treated by artificial aging is lower than T3; T3 alloy is mainly dominated by GPB region. Meanwhile, the crystal boundary displays continuously distributed fine precipitated phases; after artificial aging and creep aging treatment, a large amount of needle-shaped S′ phases precipitate inside the alloy, while there are wide precipitated phases at the crystal boundary. Wide precipitation free zones appear at the crystal boundary of artificial-aging samples, but precipitation free zones at the alloy crystal boundary of creep aging become narrower and even disappear. It can be seen that creep aging can change the precipitation features of the alloy and improve its fatigue life.

  5. Empirical Approach to Understanding the Fatigue Behavior of Metals Made Using Additive Manufacturing

    Science.gov (United States)

    Witkin, David B.; Albright, Thomas V.; Patel, Dhruv N.

    2016-08-01

    High-cycle fatigue measurements were performed on alloys prepared by powder-bed fusion additive manufacturing techniques. Selective laser melted (SLM) nickel-based superalloy 625 and electron beam melted (EBM) Ti-6Al-4V specimens were prepared as round fatigue specimens and tested with as-built surfaces at stress ratios of -1, 0.1 and 0.5. Data collected at R = -1 were used to construct Goodman diagrams that correspond closely to measured experimental data collected at R > 0. A second way to interpret the HCF data is based on the influence of surface roughness on fatigue, and approximate the surface feature size as a notch. On this basis, the data were interpreted using the fatigue notch factor k f and average stress models relating k f and stress concentration factor K t. The depth and root radius of surface features associated with fatigue crack initiation were used to estimate a K t of 2.8 for SLM 625. For Ti-6Al-4V, a direct estimate of K t from HCF data was not possible, but approximate values of k f based on HCF data and K t from crack initiation site geometry are found to explain other published EBM Ti-6Al-4V.

  6. Fatigue and fracture behavior of coiled pipes; Comportamento a fratura e fadiga de tubos bobinados

    Energy Technology Data Exchange (ETDEWEB)

    Pope, Alexandre M.; Silva, Renato M.C. [PETROBRAS, Rio de Janeiro, RJ (Brazil); Frainer, Vitor J; Tarnowski, Gabriel A.; Strohaecker, Telmo R. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil)

    2005-07-01

    The possibility of applying coiled pipes in dynamic situations, such as risers, was investigated through full scale fatigue and fracture tests. A total of sixteen X-65 pipe specimens 41/2'' Od x 0.3'' x 13', containing a bias weld at the mid length, were fatigue tested in a resonance rig at 27 Hz. Six specimens were tested in the as fabricated condition while the ten others were previously subjected to five plastic deformation cycles, simulating reeling operations.. Tests were run until a crack propagated through thickness or 10{sup 7} cycles were achieved. Two cracked specimens were fracture tested in tension. All tests were carried out at room temperature. Test results showed that the fatigue lives were above the Bs-7608 mean class 'B' curves independently whether the specimen were plastically deformed or not. Post fatigue inspection and fractographic examination revealed that fatigue cracks propagate mostly from pits or surface scratches rather than from the bias weld. The two full size tensile specimens failed by ductile fracture at 80% of the material measured strength. (author)

  7. Evidence for superior neurobiological and behavioral inhibitory control abilities in non-offending as compared to offending pedophiles.

    Science.gov (United States)

    Kärgel, Christian; Massau, Claudia; Weiß, Simone; Walter, Martin; Borchardt, Viola; Krueger, Tillmann H C; Tenbergen, Gilian; Kneer, Jonas; Wittfoth, Matthias; Pohl, Alexander; Gerwinn, Hannah; Ponseti, Jorge; Amelung, Till; Beier, Klaus M; Mohnke, Sebastian; Walter, Henrik; Schiffer, Boris

    2017-02-01

    Neurobehavioral models of pedophilia and child sexual offending suggest a pattern of temporal and in particular prefrontal disturbances leading to inappropriate behavioral control and subsequently an increased propensity to sexually offend against children. However, clear empirical evidence for such mechanisms is still missing. Using a go/nogo paradigm in combination with functional magnetic resonance imaging (fMRI) we compared behavioral performance and neural response patterns among three groups of men matched for age and IQ: pedophiles with (N = 40) and without (N = 37) a history of hands-on sexual offences against children as well as healthy non-offending controls (N = 40). As compared to offending pedophiles, non-offending pedophiles exhibited superior inhibitory control as reflected by significantly lower rate of commission errors. Group-by-condition interaction analysis also revealed inhibition-related activation in the left posterior cingulate and the left superior frontal cortex that distinguished between offending and non-offending pedophiles, while no significant differences were found between pedophiles and healthy controls. Both areas showing distinct activation pattern among pedophiles play a critical role in linking neural networks that relate to effective cognitive functioning. Data therefore suggest that heightened inhibition-related recruitment of these areas as well as decreased amount of commission errors is related to better inhibitory control in pedophiles who successfully avoid committing hands-on sexual offences against children. Hum Brain Mapp 38:1092-1104, 2017. © 2016 Wiley Periodicals, Inc.

  8. γ-Fe₂O₃ Nanocrystalline Microspheres with Hybrid Behavior of Battery-Supercapacitor for Superior Lithium Storage.

    Science.gov (United States)

    Tian, Lei-Lei; Zhang, Ming-Jian; Wu, Chao; Wei, Yi; Zheng, Jia-Xin; Lin, Ling-Piao; Lu, Jun; Amine, Khalil; Zhuang, Quan-Chao; Pan, Feng

    2015-12-02

    Maghemite (γ-Fe2O3) nanocrystalline microspheres (MNMs) self-assembled with 52 nm nanocrystals bridged with FeOOH around grain boundaries were formed by solvothermal reaction and thermal oxidation. The unique architecture endows the MNMs with the lithium storage behavior of a hybrid battery-supercapacitor electrode: initial charge capacity of 1060 mAh g(-1) at the 100 mA g(-1) rate, stable cyclic capacity of 1077.9 mAh g(-1) at the same rate after 140 cycles, and rate capability of 538.8 mAh g(-1) at 2400 mA g(-1). This outstanding performance was attributed to the nanocrystal superiority, which shortens the Li(+) diffusion paths. The mechanism of this hybrid anode material was investigated with experimental measurements and structural analysis. The results indicate that at the first discharge, the MNM nanocrystal microsphere, whose structure can buffer the volume change that occurs during lithiation/delithiation, goes through four stages: Li(+) insertion in cation vacancies, spinel-to-rocksalt transformation, Li(+) intercalation of Li(1.75+x)Fe2O3 nanocrystals, and interfacial Li storage around nanocrystal boundaries. Only the latter two stages were reversible at and after the second charging/discharging cycle, exhibiting the hybrid behavior of a battery-supercapacitor with superior lithium storage.

  9. Effect of the Tempering Temperature on Thermal Fatigue Behavior of 4Cr5MoSiV1 and 8407 Steels%4Cr5MoSiV1,8407钢的热疲劳性能

    Institute of Scientific and Technical Information of China (English)

    许珞萍; 吴晓春; 邵光杰; 闵永安

    2001-01-01

    With the self-restricting test method, the thermal fatigue behavior of 4Cr5MoSiV1 steel and 8407 steel was investigated under the same heat treatment condition. The crack morphology and fracture surface was also analyzed. The thermal fatigue process of these steels was quantitatively investigated with a thermal fatigue damage parameter. The results indicate that thermal fatigue cracks of both steels initiate at the time between 100 to 200 cycles. The initiating cracks of 8407 steel are smaller and more equable than that in 4Cr5MoSiV1 steel. Before 1600 thermal cycles, there are not obvious difference on the thermal fatigue behavior of both steels, after 1600 thermal cycles, the degree of the thermal fatigue damage of 8407 steel is lower than that of 4Cr5MoSiV1 steel. When the tempering temperature is below 640°C, the thermal fatigue behavior of 8407 steel is slightly better than that of 4Cr5MoSiV1 steel, but when the tempering temperature exceeds 640°C, the behavior of the former seems superior. The mechanism analysis of thermal fatigue reveals that the main factor affecting thermal fatigue resistance is the thermal stability and strength or hardness of steels.%采用自约束热疲劳试验方法,对比研究了相同热处理条件的4Cr5MoSiV1,8407钢的热疲劳特性,观察分析了疲劳裂纹形貌和深度,采用热疲劳损伤因子定量研究了二种钢的热疲劳过程,结果表明:两种钢的热疲劳裂纹萌生发生在100~200次之间,8407钢热疲劳裂纹的萌生较4Cr5MoSiV1钢均匀,细小;在1600次冷热循环前,二者的热疲劳损伤程度无明显差别,在1600次冷热循环后,前者的热疲劳损伤程度低于后者; 在较低的回火温度条件下,8407钢的热疲劳抗力稍优于4Cr5MoSiV1;而在高温回火时,8407钢的热疲劳抗力高于4Cr5MoSiV1钢。分析了这二种钢的热疲劳机制,指出决定材料热疲劳裂纹抗力的是钢的热稳定性和钢的强度或硬度。

  10. Effect of the Machining Processes on Low Cycle Fatigue Behavior of a Powder Metallurgy Disk

    Science.gov (United States)

    Telesman, J.; Kantzos, P.; Gabb, T. P.; Ghosn, L. J.

    2010-01-01

    A study has been performed to investigate the effect of various machining processes on fatigue life of configured low cycle fatigue specimens machined out of a NASA developed LSHR P/M nickel based disk alloy. Two types of configured specimen geometries were employed in the study. To evaluate a broach machining processes a double notch geometry was used with both notches machined using broach tooling. EDM machined notched specimens of the same configuration were tested for comparison purposes. Honing finishing process was evaluated by using a center hole specimen geometry. Comparison testing was again done using EDM machined specimens of the same geometry. The effect of these machining processes on the resulting surface roughness, residual stress distribution and microstructural damage were characterized and used in attempt to explain the low cycle fatigue results.

  11. An investigation of fracture and fatigue crack growth behavior of cast niobium aluminide intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Ye, F.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering; Farkas, D. [Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, 213 Holden Hall, Blacksburg, VA 24061-0237 (United States)

    1999-05-31

    This paper presents the results of a combined experimental and theoretical study of fracture toughness and fatigue crack growth in cast Nb-15Al-xTi (x=10, 25 and 40 at%) niobium aluminide-based intermetallics. Fracture toughness and fatigue crack growth resistance are shown to improve significantly in the cast alloy containing 40 at% Ti. The improvements in the fracture toughness of the 40Ti alloy are shown to be due to the combined effects of ligament toughening, crack-tip plasticity and crack-tip blunting. The atomistic simulations show that the increased plasticity in these alloys is associated with their higher Ti content. The micromechanisms of fatigue crack growth are also elucidated. The implications of the results are discussed for potential structural application of niobium aluminide intermetallics. (orig.) 19 refs.

  12. Cyclic Deformation Behavior and Fatigue Crack Propagation of Low Carbon Steel Prestrained in Tension

    Directory of Open Access Journals (Sweden)

    J. G. Wang

    2009-01-01

    Full Text Available The tests were performed on low carbon steel plate. In the tension fatigue tests, two angle values (ϕ=0° and ϕ=45°, ϕ is the angle between the loading and the rolling direction have been chosen. The influence of strain path change on the subsequent initial work softening rate and the saturation stress has been investigated. Dislocation microstructure was observed by transmission electron microscopy. It was found that the strain amount of preloading in tension has obviously affected the cyclic softening phenomenon and the initial cyclic softening rate. It was observed that the reloading axial stress for ϕ=45° case increased more than that of ϕ=0° case, due to the anisotropism of Q235. In the fatigue crack propagation tests, the experimental results show that with increasing the pretension deformation degree, the fatigue crack growth rate increases, especially at the near threshold section.

  13. Effect of laser shock processing on residual stress and fatigue behavior of 6061-T651 aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    REN Xu-dong; ZHANG Yong-kang; ZHOU Jian-zhong; FEN Ai-xin

    2006-01-01

    Laser shock processing is a very new technique and an emerging modern process that generates compressive stresses much deeper into the surfaces of metals or alloys. A brief parametric study of the effect of laser parameters on fatigue behavior and residual stress state generated in 6061-T651 alloy specimens was summarized. Residual stress of 6061-T651 alloy was analyzed both before and after laser processing with multishocks. The material remains in compressive residual stress of approximate lmm in depth which is approximately 10 times deeper than that can be achieved with the conventional technique, and the maximal compressive residual stress at the surface of the sampleis about -350MPa. Near the surface, yield strength and hardness are found to be increased by the laser shock. The ratio of fatigue crack initiation life for the laser-shocked to unshocked specimens is found to be 4.9 for specimens. The results clearly show that LSP is an effective surface treatment technique for improving the fatigue performance of aluminum alloys.

  14. A Critical Assessment of Cyclic Softening and Hardening Behavior in a Near- α Titanium Alloy During Thermomechanical Fatigue

    Science.gov (United States)

    Prasad, Kartik; Sarkar, Rajdeep; Rao, K. Bhanu Sankara; Sundararaman, M.

    2016-10-01

    Thermomechanical fatigue behavior of Ti-alloy Timetal 834 has been studied at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) under mechanical strain-controlled cycling. Among the temperatures studied, the alloy exhibited initial cyclic softening followed by cyclic hardening at 723 K (450 °C) in the temperature interval of 573 K to 723 K (300 °C to 450 °C). However, continuous cyclic hardening was observed at 723 K (450 °C) in 723 K to 873 K (450 °C to 600 °C). At 573 K (300 °C) and 873 K (600 °C), cyclic softening was observed in the cyclic stress response curves in both the temperature intervals. The dislocation substructure was observed to be planar in both the modes of TMF loading. Based on TEM microstructures and few unconventional fatigue tests, the observed cyclic hardening is attributed to dynamic strain aging. The reduced fatigue life at 723 K to 873 K (450 °C to 600 °C) under OP-TMF loading was attributed to the combined effect of cyclic hardening (leading to early strain localization and crack initiation), oxidation, and development of tensile mean stresses.

  15. Predicting quality of life in multiple sclerosis: accounting for physical disability, fatigue, cognition, mood disorder, personality, and behavior change.

    Science.gov (United States)

    Benedict, Ralph H B; Wahlig, Elizabeth; Bakshi, Rohit; Fishman, Inna; Munschauer, Frederick; Zivadinov, Robert; Weinstock-Guttman, Bianca

    2005-04-15

    Health-related quality of life (HQOL) is poor in multiple sclerosis (MS) but the clinical precipitants of the problem are not well understood. Previous correlative studies demonstrated relationships between various clinical parameters and diminished HQOL in MS. Unfortunately, these studies failed to account for multiple predictors in the same analysis. We endeavored to determine what clinical parameters account for most variance in predicting HQOL, and employability, while accounting for disease course, physical disability, fatigue, cognition, mood disorder, personality, and behavior disorder. In 120 MS patients, we measured HQOL (MS Quality of Life-54) and vocational status (employed vs. disabled) and then conducted detailed clinical testing. Data were analyzed by linear and logistic regression methods. MS patients reported lower HQOL (pPhysical HQOL was predicted by fatigue, depression, and physical disability. Mental HQOL was associated with only depression and fatigue. In contrast, vocational status was predicted by three cognitive tests, conscientiousness, and disease duration (p<0.05). Thus, for the first time, we predicted HQOL in MS while accounting for measures from these many clinical domains. We conclude that self-report HQOL indices are most strongly predicted by measures of depression, whereas vocational status is predicted primarily by objective measures of cognitive function. The findings highlight core clinical problems that merit early identification and further research regarding the development of effective treatment.

  16. Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure

    Directory of Open Access Journals (Sweden)

    Ungyu Paik

    2013-08-01

    Full Text Available The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF and low-pressure plasma spray (LPPS methods showed a partial cracking (and/or delamination and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50% after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF.

  17. The potential significance of microalloying with niobium in governing very high cycle fatigue behavior of bainite/martensite multiphase steels

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, P., E-mail: zhaoping12@mails.tsinghua.edu.cn [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Beijing Iron & Steel Research Institute, Special Steel Institute, Beijing 100081 (China); Cheng, C.; Gao, G.; Hui, W. [Materials Science & Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Misra, R.D.K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas, El Paso 500 W. University Avenue, El Paso, TX 79968-0520 (United States); Bai, B.; Weng, Y. [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)

    2016-01-05

    We elucidate here the effect of microalloying with niobium (Nb) on very high cycle fatigue (VHCF) behavior in high-strength C–Mn–Si–Cr bainite/martensite (B/M) multiphase steels studied through ultrasonic fatigue testing. The tensile strength (R{sub m}) and fatigue limit strength after 10{sup 9} cycles (σ{sub w9}) and in the non-failure condition of the steel microalloyed with Nb were 1640 MPa and 900 MPa, respectively. Thus, the value of σ{sub w9}/R{sub m} exceeded in comparison to conventional steels and was approximate 0.55. Three types of failure modes were observed in Nb-bearing steels depending on the surface condition, inclusion, and the matrix microstructure, i.e., surface defect-induced failure mode (S-mode), inclusion-induced failure mode (I-mode), and non-inclusion induced failure mode (N-mode). Only two failure modes were observed in Nb-free steels, the S-mode and the N-mode. The study clearly suggests that Nb had a distinct effect on the VHCF properties of B/M steels. The VHCF limit of Nb-bearing steel was enhanced by 200 MPa because of refinement of the microstructure and pinning of dislocations by randomly distributed nanometer-sized Nb(C, N) precipitates. It is underscored that microalloying with Nb is a potential approach to enhance VHCF properties in advanced high-strength steels.

  18. Cancer-Related Fatigue and Rehabilitation: A Randomized Controlled Multicenter Trial Comparing Physical Training Combined With Cognitive-Behavioral Therapy With Physical Training Only and With No Intervention

    OpenAIRE

    Van Weert, E.; May, A. M.; Korstjens, I.; Post, W.J.; van der Schans, C. P.; van den Borne, B; Mesters, I.; Ros, W J G; Hoekstra-Weebers, J.E.H.M.

    2010-01-01

    textabstractBackground. Research suggests that cancer rehabilitation reduces fatigue in survivors of cancer. To date, it is unclear what type of rehabilitation is most beneficial. Objective. This randomized controlled trial compared the effect on cancerrelated fatigue of physical training combined with cognitive behavioral therapy with physical training alone and with no intervention. Design. In this multicenter randomized controlled trial, 147 survivors of cancer were randomly assigned to a ...

  19. Perceptions of Leadership Style: Superior and Subordinate Descriptions of Decision-Making Behavior

    Science.gov (United States)

    Jago, Arthur G.; Vroom, Victor H.

    1975-01-01

    This research concerns the level of agreement among subordinates reporting to the same leader in their descriptions of his behavior. (Available from the Comparative Administration Research Institute, Graduate School of Business Administration, Kent State University, Kent, OH 44242; $12.00 annually) (Author/MLF)

  20. Effects of cooling rate and stabilization annealing on fatigue behavior of β-processed Ti-6Al-4V alloys

    Science.gov (United States)

    Seo, Wongyu; Jeong, Daeho; Lee, Dongjun; Sung, Hyokyung; Kwon, Yongnam; Kim, Sangshik

    2017-07-01

    The effects of stabilization annealing and cooling rate on high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors of β-processed Ti64 alloys were examined. After β-process heating above β transus, two different cooling rates of air cooling (β-annealing) and water quenching (β-quenching) were utilized. Selected specimens were then underwent stabilization annealing. The tensile tests, HCF and FCP tests on conducted on the β-processed Ti64 specimens with and without stabilization annealing. No notable microstructural and mechanical changes with stabilization annealing was observed for the β-annealed Ti64 alloys. However, significant effect of stabilization annealing was found on the FCP behavior of β-quenched Ti64 alloys, which appeared to be related to the built-up of residual stress after quenching. The mechanical behavior of β-processed Ti64 alloys with and with stabilization annealing was discussed based on the micrographic examination, including crack growth path and crack nucleation site, and fractographic analysis.

  1. Safety behaviors and sleep effort predict sleep disturbance and fatigue in an outpatient sample with anxiety and depressive disorders

    Science.gov (United States)

    Fairholme, Christopher P.; Manber, Rachel

    2015-01-01

    Objective Theoretical and empirical support for the role of dysfunctional beliefs, safety behaviors, and increased sleep effort in the maintenance of insomnia has begun to accumulate. It is not yet known how these factors predict sleep disturbance and fatigue occurring in the context of anxiety and mood disorders. It was hypothesized that these three insomnia-specific cognitive–behavioral factors would be uniquely associated with insomnia and fatigue among patients with emotional disorders after adjusting for current symptoms of anxiety and depression and trait levels of neuroticism and extraversion. Methods Outpatients with a current anxiety or mood disorder (N = 63) completed self-report measures including the Dysfunctional Beliefs About Sleep Scale (DBAS), Sleep-Related Safety Behaviors Questionnaire (SRBQ), Glasgow Sleep Effort Scale (GSES), Pittsburgh Sleep Quality Index (PSQI), NEO Five-Factor Inventory (FFI), and the 21-item Depression Anxiety and Stress Scale (DASS). Multivariate path analysis was used to evaluate study hypotheses. Results SRBQ (B = .60, p anxiety and depressive disorders with disturbed sleep. PMID:24529043

  2. Short fatigue cracks growth and closure behavior in an austenitic stainless steel at 600 C and 650 C

    Energy Technology Data Exchange (ETDEWEB)

    Polvora, J.P.; Laiarinandrasana, L.; Drubay, B.; Piques, R.; Martelet, B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)

    1995-12-31

    In this work, following fatigue crack growth tests carried out at the CEN-SACLAY (AMORFIS program) by Laiarinandrasana (1994) on 316 L(N) CT specimens at 650{sup 0}C and 600{sup 0}C, short crack behavior of cracks emanating from machined notches is investigated. Experimental results are presented and discussions are directed to notch plasticity effect in relation with variations in crack opening stress intensity factor, K{sub op}, with crack lenght (author). 12 refs., 5 figs., 2 tab.

  3. Effects of Exercise on Behavior and Peripheral Blood Lymphocyte Apoptosis in a Rat Model of Chronic Fatigue Syndrome

    Institute of Scientific and Technical Information of China (English)

    邹军; 苑建齐; 吕爽; 屠嘉衡

    2010-01-01

    This study examined the effects of exercise on behavior and peripheral blood leukocyte apoptosis in a rat model of chronic fatigue syndrome(CFS).Thirty-six healthy male Sprague-Dawley rats were equally randomized into 3 groups:the control group,CFS model group and the exercise group in terms of body weight.A total of 25 rats entered the final statistical analysis due to 11 deaths during the study.CFS model was established by subjecting the rats in CFS model group and exercise group to electric shock,chronic...

  4. Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G., E-mail: agang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

    2016-02-08

    Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

  5. Superior 'theory of mind' in borderline personality disorder: an analysis of interaction behavior in a virtual trust game.

    Science.gov (United States)

    Franzen, Nele; Hagenhoff, Meike; Baer, Nina; Schmidt, Ariane; Mier, Daniela; Sammer, Gebhard; Gallhofer, Bernd; Kirsch, Peter; Lis, Stefanie

    2011-05-15

    To gain further insight into interpersonal dysfunction in Borderline Personality Disorder (BPD) we investigated the effects of emotional cues and the fairness of a social partner on the ability to infer other peoples' intentions in a virtual social exchange. 30 BPD patients and 30 nonpatients were asked to play a multiround trust game with four virtual trustees. The trustees varied in regard to fairness and presence of emotional facial cues which were both linked to repayment ratio. BPD patients adjusted their investment to the fairness of their partner. In contrast, nonpatients disregarded the trustees' fairness in the presence of emotional facial expressions. Both groups performed equally in an emotion recognition task and assessed the trustees' fairness comparably. When the unfair trustee provided emotional cues, BPD patients assessed their own behavior as more fair, while the lack of cues led patients to assess their own behavior as unfair. BPD patients are superior in the attribution of mental states to interaction partners when emotional cues are present. While the emotional expressions of a partner dominated the exchange behavior in nonpatients, BPD patients used the objective fairness of their social counterparts to guide their own behavior despite the existence of emotional cues. Copyright © 2010 Elsevier Ltd. All rights reserved.

  6. Price Limit, Superior Information and Investor Behavior: Evidence from China Stock Market

    Institute of Scientific and Technical Information of China (English)

    FAN Li-min; LONG Zheng-ping; ZHU Bao-jun

    2007-01-01

    The mechanism of price limit impacts on informed traders' behavior. To find out what effects related to price limit, three hypotheses caused by price limit are analyzed.Comprehensive method of event study and comparative grouping is used to test the performance of price limit in Chinese stock market. The result of test indicates that price limit policy impedes fulfillment of traders and delays the discovery of stock price so it should be abolished.

  7. Cryogenic fatigue and stress-strain behavior of a fibre metal laminate

    NARCIS (Netherlands)

    Camp, W.V.D.; Dhallé, M.M.J.; Wessel, W.A.J.; Warnet, L.; Atli-Veltin, B.; Putten, S.V.D.; Dam, J.A.M.; Ter Brake, H.J.M.

    2015-01-01

    This paper reports on the cryogenic fatigue life of Al 2024 / Stycast 2850 FT composite sandwiches loaded under cyclic strain, as well as on the strength of their constituent materials at 77 K. These Fibre Metal Laminate (FML) specimen serve as a model for an alternative class of cryogenic

  8. Impact and residual fatigue behavior of ARALL and AS6/5245 composite materials

    Science.gov (United States)

    Johnson, W. S.

    1986-01-01

    Aramide fiber reinforced aluminum laminates (ARALL) represent a cross between resin matrix composites and metals. The purpose of this study was to evaluate the impact sensitivity of this concept. Two types of ARALL (7075 aluminum prestrained and 2024 aluminum not prestrained) were tested through static indentation and the results compared to sheet 2024-T3 and 7075-T6 aluminum alloys. A state-of-the-art composite (AS6/5245) was also tested and compared to the ARALL. Further, the two types of ARALL material and the composite were dynamically impacted at two energy levels and fatigue tested to determine residual fatigue strength. Both forms of the ARALL material had worse impact resistance than monolithic sheet aluminum. The ARALL material made with 2024-T3 aluminum had better impact resistance than did the laminates made with 7075-T6 aluminum. The ARALL materials are at least equal to the composite material in impact damage resistance and are better for impact detection. The composite material has higher residual fatigue strength after impact than the ARALL material and is 25 percent lighter. The prestraining of the ARALL greatly reduces the fatigue growth of impact damage.

  9. Cryogenic fatigue and stress-strain behavior of a fibre metal laminate

    NARCIS (Netherlands)

    Camp, W.V.D.; Dhallé, M.M.J.; Wessel, W.A.J.; Warnet, L.; Atli-Veltin, B.; Putten, S.V.D.; Dam, J.A.M.; Ter Brake, H.J.M.

    2015-01-01

    This paper reports on the cryogenic fatigue life of Al 2024 / Stycast 2850 FT composite sandwiches loaded under cyclic strain, as well as on the strength of their constituent materials at 77 K. These Fibre Metal Laminate (FML) specimen serve as a model for an alternative class of cryogenic structura

  10. Computer simulation on fatigue behavior of cemented hip prostheses: a physiological model.

    Science.gov (United States)

    Hung, Jui-Pin; Chen, Jian-Horng; Chiang, Hsiu-Lu; Wu, James Shih-Shyn

    2004-11-01

    This paper is concerned with the investigation on the fatigue failure of implant fixation by numerical approaches. A computer algorithm based on finite element analysis and continuum damage mechanics was proposed to quantify the fatigue damage rate of cement mantle under physiological conditions. In examining the interfacial debonding effect, the interface elements were introduced at cement-stem interfaces and calibrated with the increase of loading cycles. Current results reveal that the major sites for failure initiation are in the proximal anterior-medial regions and at the distal prosthesis tip, which clearly demonstrate the same failure scenario as observed in clinical studies. Such fatigue failures not only result in the corruption of cement-stem interfaces, but also greatly affect the cement stress distribution and the damage rate in subsequent loading cycles. Another significant result is that the predicted damage rate increases steadily with gait cycles. This trend in damage development is consistent with the findings obtained from fatigue tests available in literature. It is anticipated that presented methodology can serve as a pre-clinical validation of cemented hip prostheses.

  11. A New Paradigm of Fatigue Variability Behavior and Implications for Life Prediction (Preprint)

    Science.gov (United States)

    2006-06-01

    31] S. Suresh, Fatigue of Materials, Cambridge University Press, 1991. [32] A. S. Beranger, X. Feaugas, and M. Clavel , Mater. Sci. Eng., Vol...A172, p. 31, 1993. [33] X. Feaugas and M. Clavel , Acta Materialia, Vol. 45, p. 2685, 1997. [34] D. L. McDowell, K. Gall, M. F. Horstememyer, and J. Fan

  12. The Effect of Microstructure on Fretting Fatigue Behavior of Nickel Alloy IN-100

    Science.gov (United States)

    2007-03-01

    2317, 2004 115 27. Sondhi, S.K. et al. Tension-compression creep asymmetry in a turbine disc superalloy : Roles if internal stress and thermal...82 5.6 Effect of Grain Size on Fatigue in Nickel-based Superalloys 83...done on correlating changes in microstructure to changes in strength for superalloys . Huther and Reppich [18] suggest the following formula for

  13. Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite-pearlite and ferrite-bainite microstructures

    Energy Technology Data Exchange (ETDEWEB)

    Guan, Mingfei [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Hao, E-mail: yhzhmr@126.com [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-01-01

    The roles of microstructure types in fatigue crack growth behaviors in ferrite-pearlite steel and ferrite-bainite steel were investigated. The ferrite-bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite-pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F-P steel could become unstable more ealier compared with that in F-B steel. The fatigue cracks in ferrite-pearlite were more tortuous and could propagate more freely than that in ferrite-bainite microstructures. However, frequent crack branching were observed in ferrite-bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range ({Delta}K) for F-P and F-B steels was discussed within the Paris region. It was shown that FCG rate of F-P steel was higher than that of F-B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

  14. Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA's High Temperature, High Speed Turbine Seal Test Rig

    Science.gov (United States)

    Delgado, Irebert R.; Steinetz, Bruce M.; Rimnac, Clare M.; Lewandowski, John J.

    2008-01-01

    The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA s Turbine Seal Test Facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current detection thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles when operated at maximum operating conditions.

  15. Influences of post weld heat treatment on fatigue crack growth behavior of TIG welding of 6013 T4 aluminum alloy joint (Part 1. Fatigue crack growth across the weld metal)

    Energy Technology Data Exchange (ETDEWEB)

    Haryadi, Gunawan Dwi; Kim, Seon Jin [Pukyong National University, Busan (Korea, Republic of)

    2011-09-15

    The present study evaluates the influences of PWHT on FCG behavior and tensile properties of TIG butt welded Al 6013-T4 sheets. Crack propagation tests were carried out on compact tension (CT) specimens. The T82 heat treatment was varied in three artificial aging times (soaking) of 6, 18 and 24 hours. The results of T82 heat treatment with artificial aging variations were tested for their fatigue crack growth rates at the main metal zone, the heat-affected zone (HAZ), and the welded metal zone. It has been observed that the various agings in heat treatment T82 are sensitive to the mechanical properties (fatigue crack growth rate test, tensile test). The results show that PWHT-T82 for 18 hours aging is the highest fatigue resistance, while the aging 18 hours provided the highest tensile test result.

  16. Fatigue behavior of Ti–6Al–4V alloy in saline solution with the surface modified at a micro- and nanoscale by chemical treatment

    Energy Technology Data Exchange (ETDEWEB)

    Claros, Cesar Adolfo Escobar; Oliveira, Diego Pedreira; Campanelli, Leonardo Contri; Pereira da Silva, Paulo Sergio Carvalho; Bolfarini, Claudemiro

    2016-10-01

    This work evaluated the influence of the surface modification using acid etching combined with alkaline treatment on the fatigue strength of Ti–6Al–4V ELI alloy. The topography developed by chemical surface treatments (CST) was examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased roughness and effective surface area were investigated and compared with the Ti–6Al–4V samples without modification. Surface composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistance of polished and modified surfaces was determined by stepwise load increase tests and staircase test method. Light microscopy and SEM were employed to examine the fracture surface of the tested specimens. According to the results, a similar fatigue behavior was found and a negligible difference in the fatigue crack nucleation was observed for the Ti–6Al–4V with CST in comparison to the samples without treatment. - Highlights: • Fatigue behavior of Ti–6Al–4V with the surface modified by chemical treatments • The topography developed did not induce differences in the fatigue resistance. • Untreated and chemically treated surfaces presented fractographic similarities.

  17. Evaluation of Orientation Dependence of Fracture Toughness and Fatigue Crack Propagation Behavior of As-Deposited ARCAM EBM Ti-6Al-4V

    Science.gov (United States)

    Seifi, Mohsen; Dahar, Matthew; Aman, Ron; Harrysson, Ola; Beuth, Jack; Lewandowski, John J.

    2015-03-01

    This preliminary work documents the effects of test orientation with respect to build and beam raster directions on the fracture toughness and fatigue crack growth behavior of as-deposited EBM Ti-6Al-4V. Although ASTM/ISO standards exist for determining the orientation dependence of various mechanical properties in both cast and wrought materials, these standards are evolving for materials produced via additive manufacturing (AM) techniques. The current work was conducted as part of a larger America Makes funded project to begin to examine the effects of process variables on the microstructure and fracture and fatigue behavior of AM Ti-6Al-4V. In the fatigue crack growth tests, the fatigue threshold, Paris law slope, and overload toughness were determined at different load ratios, R, whereas fatigue precracked samples were tested to determine the fracture toughness. The as-deposited material exhibited a fine-scale basket-weave microstructure throughout the build, and although fracture surface examination revealed the presence of unmelted powders, disbonded regions, and isolated porosity, the resulting mechanical properties were in the range of those reported for cast and wrought Ti-6Al-4V. Remote access and control of testing was also developed at Case Western Reserve University to improve efficiency of fatigue crack growth testing.

  18. A study of elevated temperature testing techniques for the fatigue behavior of PMCS: Application to T650-35/AMB21

    Science.gov (United States)

    Gyekenyesi, Andrew L.; Gastelli, Michael G.; Ellis, John R.; Burke, Christopher S.

    1995-01-01

    An experimental study was conducted to investigate the mechanical behavior of a T650-35/AMB21 eight-harness satin weave polymer composite system. Emphasis was placed on the development and refinement of techniques used in elevated temperature uniaxial PMC testing. Issues such as specimen design, gripping, strain measurement, and temperature control and measurement were addressed. Quasi-static tensile and fatigue properties (R(sub sigma) = 0.1) were examined at room and elevated temperatures. Stiffness degradation and strain accumulation during fatigue cycling were recorded to monitor damage progression and provide insight for future analytical modeling efforts. Accomplishments included an untabbed dog-bone specimen design which consistently failed in the gage section, accurate temperature control and assessment, and continuous in-situ strain measurement capability during fatigue loading at elevated temperatures. Finally, strain accumulation and stiffness degradation during fatigue cycling appeared to be good indicators of damage progression.

  19. The fatigue and corrosion fatigue behavior of welded Inconel 625 alloy employed in off-shore platforms; Avaliacao do comportamento a fadiga e a corrosao-fadiga de juntas soldadas da liga Inconel 625 testada para uso em plaaformas off-shore

    Energy Technology Data Exchange (ETDEWEB)

    Pfingstag, M.E.; Schroeder, R.M.; Mueller, I.L. [Universidade Federal do Rio Grande do Sul (LAPEC/UFRGS), Porto Alegre, RS (Brazil). Dept. de Metalurgia. Lab. de Pesquisa em Corrosao], e-mail: maiquel10@walla.com

    2006-07-01

    The fatigue and corrosion fatigue behavior of welded Inconel 625 employed live like risers in off-shore platforms was studied. These risers may be employed integrally of this alloy, or combined with API 52 X60 steel in the form of 'Clads'. One of the most susceptible points in .these structures is the circumferential weld that joint the pipes together. In these regions, stresses and defects are generated by the welding process, and these material remind in contact with aggressive species like, chlorides and Co{sub 2} . Polarization curves, slow strain rate fatigue and corrosion fatigue tests were used to characterize the Inconel alloy behavior. In the welded deposit condition, this alloy shows an excellent resistance corrosion and a good fatigue and corrosion-fatigue behavior.(author)

  20. Creep and creep-fatigue behavior of high chromium steel weldment

    Institute of Scientific and Technical Information of China (English)

    Yukio TAKAHASHI; Masaaki TABUCHI

    2011-01-01

    Manuscript received I December 2010; in revised form 9 March 2011Strength of welded joints of high chromium steels is one of the important concerns for fabricators and operators of ultra supercritical thermal power plants. A number of creep as well as creep-fatigue tests with tensile hold have been carried out on the welded joints of two types of high chromium steels widely used in Japan, I.e. Grade 91 and 122 steels. It was found that failure occurred in fine grain heat-affected zone in all the creep-fatigue tests, even at a relatively low temperature and fairly short time where failure occurred in plain base metal region in simple creep testing. Four procedures were used to predict failure lives and their results were compared with the test results. A newly proposed energy-based approach gave the best estimation of failure life, without respect of the material and temperature.

  1. Fatigue Behavior of Oil Jet Peened Aluminum Alloy, AA 6063-T6

    Science.gov (United States)

    Grinspan, Alphonse Sahaya; Gnanamoorthy, Rajappa

    Oil jet peening is a new surface modification process developed for the introduction of compressive residual stresses. This paper describes the effect of oil jet peening on the fatigue performance of aluminum alloy, AA 6063-T6. Specimens were peened at an oil injection pressure of 40 MPa with various nozzle-traveling velocities. Each impact of oil droplet generates an indentation on the surface of specimen. The surface roughness increases with decreasing nozzle-traveling velocity. The maximum compressive residual stress developed is about 75% of yield strength. Fatigue life depends on the compressive residual stress as well as surface roughness of oil jet peened specimens. Fracture mechanism of unpeened and oil jet peened specimens were studied using optical and scanning electron microscopes.

  2. Superior pseudocapacitive behavior of confined lignin nanocrystals for renewable energy-storage materials.

    Science.gov (United States)

    Kim, Sung-Kon; Kim, Yun Ki; Lee, Hyunjoo; Lee, Sang Bok; Park, Ho Seok

    2014-04-01

    Strong demand for high-performance energy-storage devices has currently motivated the development of emerging capacitive materials that can resolve their critical challenge (i.e., low energy density) and that are renewable and inexpensive energy-storage materials from both environmental and economic viewpoints. Herein, the pseudocapacitive behavior of lignin nanocrystals confined on reduced graphene oxides (RGOs) used for renewable energy-storage materials is demonstrated. The excellent capacitive characteristics of the renewable hybrid electrodes were achieved by synergizing the fast and reversible redox charge transfer of surface-confined quinone and the interplay with electron-conducting RGOs. Accordingly, pseudocapacitors with remarkable rate and cyclic performances (~96 % retention after 3000 cycles) showed a maximum capacitance of 432 F g(-1), which was close to the theoretical capacitance of 482 F g(-1) and sixfold higher than that of RGO (93 F g(-1)). The chemical strategy delineated herein paves the way to develop advanced renewable electrodes for energy-storage applications and understand the redox chemistry of electroactive biomaterials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Thermomechanical Fatigue Behavior of Coated and Uncoated Enhanced SiC/SiC Studied

    Science.gov (United States)

    1996-01-01

    Thermomechanical fatigue (TMF) testing provides a method of evaluating candidate continuous-fiber-reinforced ceramic composites under thermal and mechanical loading conditions. Although these tests are complicated, they provide a reasonable approximation of the combined thermal and mechanical loads that will be experienced by the material in service. The resulting data will be used to develop life-prediction models as well as to aid materials development.

  4. Fatigue crack growth rate (FCGR) behavior of nicalon/SiC composites

    Energy Technology Data Exchange (ETDEWEB)

    Miriyala, N.; Liaw, P.K.; Yu, N. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1995-04-01

    The objective is to develop a fundamental understanding of fatigue crack growth phenomenon in Nicalon/SiC composites. Ultrasonic measurements were continued on the Nicalon/SiC composite specimens to correlate elastic moduli with percentage porosity in the in-plane as well as through-thickness directions. A micromechanics model based on periodic microstructure was developed to predict the elastic stiffness constants of the Nicalon/SiC composites. The predicted values were in good agreement with the experimental results.

  5. Assessment of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720

    Science.gov (United States)

    Gabb, Tomothy P.; Bonacuse, Peter J.; Ghosn, Louis J.; Sweeney, Joseph W.; Chatterjee, Amit; Green, Kenneth A.

    2000-01-01

    The fatigue lives of modem powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538 C (1000 F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions. Significant variations in life were observed as functions of the disk processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio R(sub epsilon) = epsilon(sub min)/epsilon(sub max) of 0 were different from those in tests at a strain ratio of -1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.

  6. Fatigue behavior of highly porous titanium produced by powder metallurgy with temporary space holders

    Energy Technology Data Exchange (ETDEWEB)

    Özbilen, Sedat [Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK), 52425 Jülich (Germany); Gazi University, Faculty of Technology, Department of Metallurgical and Materials Engineering, Teknikokullar, Ankara (Turkey); Liebert, Daniela [Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK), 52425 Jülich (Germany); Beck, Tilmann [Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK), 52425 Jülich (Germany); University of Kaiserslautern, Lehrstuhl für Werkstoffkunde (WKK), D-67663 Kaiserslautern (Germany); Bram, Martin, E-mail: m.bram@fz-juelich.de [Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK), 52425 Jülich (Germany)

    2016-03-01

    Porous titanium cylinders were produced with a constant amount of temporary space holder (70 vol.%). Different interstitial contents were achieved by varying the starting powders (HDH vs. gas atomized) and manufacturing method (cold compaction without organic binders vs. warm compaction of MIM feedstocks). Interstitial contents (O, C, and N) as a function of manufacturing were measured by chemical analysis. Samples contained 0.34–0.58 wt.% oxygen, which was found to have the greatest effect on mechanical properties. Quasi-static mechanical tests under compression at low strain rate were used for reference and to define parameters for cyclic compression tests. Not unexpectedly, increased oxygen content increased the yield strength of the porous titanium. Cyclic compression fatigue tests were conducted using sinusoidal loading in a servo-hydraulic testing machine. Increased oxygen content was concomitant with embrittlement of the titanium matrix, resulting in significant reduction of compression cycles before failure. For samples with 0.34 wt.% oxygen, R, σ{sub min} and σ{sub max} were varied systematically to estimate the fatigue limit (~ 4 million cycles). Microstructural changes induced by cyclic loading were then characterized by optical microscopy, SEM and EBSD. - Highlights: • Systematic variation of the oxygen content from 0.34 to 0.58 wt.%. • Systematic study of the relationship between fatigue limit and oxygen content. • Critical oxygen equivalent seems to be 0.35 wt.% to avoid embrittlement. • Identification of the failure modes by light microscopy, SEM and EBSD.

  7. Research review of low-cycle fatigue behavior of steel brace%钢支撑低周疲劳性能研究综述

    Institute of Scientific and Technical Information of China (English)

    于海丰; 张学辉; 李其廉

    2011-01-01

    总结了国际上有关钢支撑低周疲劳性能试验及有限元研究方面的现状,指出了钢支撑低周疲劳性能研究的方向。%Low-cycle fatigue behavior research of the steel brace is prerequisite to the understanding of the seismic performance of concentrically braced frame with moment resisting frame dual systems. In this paper, the current test and finite element research in the low-cycle fatigue behavior of the steel brace is reviewed and the further research direction is pointed out.

  8. 再生混凝土弯折疲劳性能%Investigation on fatigue behavior of recycled aggregate concrete under flexure loading

    Institute of Scientific and Technical Information of China (English)

    肖建庄; 李宏; 李龙

    2012-01-01

    The fatigue behaviors of recycled aggregate concrete (RAC) with 100% recycled coarse aggregate (RCA) replacement percentage under flexure loading are tested. The fatigue failure pattern and fatigue strength are analyzed. Based on the analysis of fatigue strain variation in different heights of prism as well as the neutral axis depth, the fatigue damage evolution of RAC is investigated. On the basis of the experimental results and continuum damage mechanics, a flexural fatigue damage model is proposed. The results show that the failure pattern under fatigue flexure loading is basically the same as that under static loading, and a linear relationship exists between the logarithm of fatigue life N of RAC and the stress level S under flexure loading. The flexural fatigue damage model is good enough to verify the fatigue test results. It can be applied to the theoretical and numerical analyses of the RAC fatigue behavior under flexure loading.%完成了再生粗骨料取代率为100%的再生混凝土弯折疲劳试验,对其疲劳破坏现象和疲劳强度进行了分析.通过分析疲劳荷载下再生混凝土棱柱体在不同截面高度处的疲劳应变况以及其中性轴的变化情况,研究了再生混凝土弯折疲劳损伤演化过程.基于试验结果和连续损伤力学,提出了一个再生混凝土弯折疲劳损伤模型.结果表明,弯折疲劳破坏情况与静载作用时基本相似,再生混凝土弯折疲劳S-N曲线呈单对数直线关系.再生混凝土弯折疲劳损伤模型可以很好地验证疲劳试验结果,可用来对再生混凝土梁疲劳性能进行理论和数值分析.

  9. Cognitive behavioral therapy for insomnia, but not armodafinil, improves fatigue in cancer survivors with insomnia: a randomized placebo-controlled trial.

    Science.gov (United States)

    Heckler, Charles E; Garland, Sheila N; Peoples, Anita R; Perlis, Michael L; Shayne, Michelle; Morrow, Gary R; Kamen, Charles; Hoefler, Jenine; Roscoe, Joseph A

    2016-05-01

    Fatigue is a prevalent, distressing side effect of cancer and cancer treatment which commonly coexists with insomnia. Cognitive behavioral therapy for insomnia (CBT-I) has been shown to improve insomnia in cancer patients, but less is known about its ability to impact fatigue. This work is the analysis for a secondary aim of a four-arm randomized controlled trial (RCT) study assessing the combined and comparative effect of CBT-I and a wakefulness-promoting agent, armodafinil (A), to improve sleep and daytime functioning in cancer survivors. Herein, we examine the effect of CBT-I, with and without A, on fatigue in cancer survivors. This study was a four-arm factorial study with CBTI-I (yes/no) versus A (yes/no). It consisted of 96 cancer survivors (average age 56 years; 88 % female; 68 % breast cancer). Fatigue was assessed by the brief fatigue inventory (BFI) and the FACIT-Fatigue scale. The analysis assessed the additive effects of CBT-I and A and possible non-additive effects where the effect of CBT-I changes depending on the presence or absence of A. Analyses adjusting for baseline differences showed that CBT-I improved fatigue as measured by two separate scales (BFI: P = 0.002, Std. error = 0.32, effect size (ES) = 0.46; FACIT-Fatigue: P  0.40) nor did the drug influence the efficacy of CBT-I. Structural equation analysis revealed that reductions in insomnia severity were directly responsible for improving cancer-related fatigue. CBT-I with and without armodafinil resulted in a clinically and statistically significant reduction of subjective daytime fatigue in cancer survivors with chronic insomnia. Armodafinil did not improve cancer-related fatigue (CRF) and did not change the efficacy of CBT-I. Patients reporting CRF should be screened and, if indicated, treated for insomnia as part of a comprehensive fatigue management program.

  10. Crack growth behavior under creep-fatigue conditions using compact and double edge notch tension-compression specimens

    Science.gov (United States)

    Narasimha Chary, Santosh Balaji

    inspection of fatigue surfaces, it has been found that that better alignment control procedures are needed to ensure symmetric crack fronts for the DEN(T-C) specimen. Creep-fatigue crack growth tests were conducted on 9Cr-1Mo (P91) steels at 625°C with various hold times. These tests were conducted using C(T) specimens under constant load amplitude conditions (tension-tension) and DEN(T-C) specimens under displacement like conditions (tension-compression). Crack growth data generated under creep-fatigue conditions using standard C(T) specimens correlated well with crack growth data generated using DEN(T-C) specimens. The crack growth rates per cycle increased significantly with increase in hold time when crack growth data were plotted with the cyclic stress intensity parameter, Delta-K. A transient behavior in the initial portion of da/dN versus Delta-K plots were observed for the hold time tests, as reported previously by several other researchers. It is shown for the C(T) specimens that the creep-fatigue interactions during crack growth for various hold times are represented better by the (Ct)avg parameter implying that the P91 steel behaves in a creep-ductile manner. Significant differences (factors of 2 to 5) were observed between the calculated values of (Ct)avg and those based on measured values of force-line deflection. It is also shown that there is a high risk of obtaining invalid data in longer hold time tests under force-control conditions. The usefulness of DEN(T-C) specimens for crack growth studies under displacement controlled conditions to combat ratcheting problems in tests conducted under load conditions is established. The tests conditions for the round-robin program on creep-fatigue crack growth testing in support of ASTM E-2760 are finalized. Further developments needed in creep-fatigue crack growth testing are also presented.

  11. Distractor evoked deviations of saccade trajectory are modulated by fixation activity in the superior colliculus: computational and behavioral evidence.

    Directory of Open Access Journals (Sweden)

    Zhiguo Wang

    Full Text Available Previous studies have shown that saccades may deviate towards or away from task irrelevant visual distractors. This observation has been attributed to active suppression (inhibition of the distractor location unfolding over time: early in time inhibition at the distractor location is incomplete causing deviation towards the distractor, while later in time when inhibition is complete the eyes deviate away from the distractor. In a recent computational study, Wang, Kruijne and Theeuwes proposed an alternative theory that the lateral interactions in the superior colliculus (SC, which are characterized by short-distance excitation and long-distance inhibition, are sufficient for generating both deviations towards and away from distractors. In the present study, we performed a meta-analysis of the literature, ran model simulations and conducted two behavioral experiments to further explore this unconventional theory. Confirming predictions generated by the model simulations, the behavioral experiments show that a saccades deviate towards close distractors and away from remote distractors, and b the amount of deviation depends on the strength of fixation activity in the SC, which can be manipulated by turning off the fixation stimulus before or after target onset (Experiment 1, or by varying the eccentricity of the target and distractor (Experiment 2.

  12. Distractor evoked deviations of saccade trajectory are modulated by fixation activity in the superior colliculus: computational and behavioral evidence.

    Science.gov (United States)

    Wang, Zhiguo; Theeuwes, Jan

    2014-01-01

    Previous studies have shown that saccades may deviate towards or away from task irrelevant visual distractors. This observation has been attributed to active suppression (inhibition) of the distractor location unfolding over time: early in time inhibition at the distractor location is incomplete causing deviation towards the distractor, while later in time when inhibition is complete the eyes deviate away from the distractor. In a recent computational study, Wang, Kruijne and Theeuwes proposed an alternative theory that the lateral interactions in the superior colliculus (SC), which are characterized by short-distance excitation and long-distance inhibition, are sufficient for generating both deviations towards and away from distractors. In the present study, we performed a meta-analysis of the literature, ran model simulations and conducted two behavioral experiments to further explore this unconventional theory. Confirming predictions generated by the model simulations, the behavioral experiments show that a) saccades deviate towards close distractors and away from remote distractors, and b) the amount of deviation depends on the strength of fixation activity in the SC, which can be manipulated by turning off the fixation stimulus before or after target onset (Experiment 1), or by varying the eccentricity of the target and distractor (Experiment 2).

  13. Softening Behavior of Hardness and Surface Fatigue of Rolling-Sliding Contact in the Case of Developed Alloy Steels

    Science.gov (United States)

    Redda, Daniel Tilahun; Nakanishi, Tsutomu; Deng, Gang

    To get high performance, downsizing and weight saving of the power transmission systems, the improvement of machine elements has been required. In this study, case-carburized gear materials for a high load-carrying capacity were developed. Low-alloyed steels with 1%Cr-0.2%Mo, 1%Cr-0.2%Mo-1%Si and 1%Cr-0.2%Mo-2%Ni (Cr-Mo steel, Cr-Mo-Si steel and Cr-Mo-Ni steel) were melted in a hypoxia vacuum. Test rollers were made of the developed steels, and they were carburized (Type A and Type B), hardened and tempered. Heating retention tests were carried out to investigate the softening behavior of hardness at high heating temperatures in the case of the developed steels. Roller tests were conducted under the rolling-sliding contact and high-load conditions to study the surface fatigue of the developed steels. From the obtained test results, it was found that the softening behavior of surface hardness at high temperatures in the cases of Cr-Mo-Si steel (Type A) and Cr-Mo-Ni steel (Type B) is lower than that in the cases of Cr-Mo steel (Type A) and Cr-Mo steel (Type B). In the cases of Cr-Mo-Si steel (A) and Cr-Mo-Ni steel (B), micro- and small-pitting area ratios are smaller and large-pitting life is longer than those in the cases of Cr-Mo steel(A) and Cr-Mo steel(B) under the same carburizing treatment method and high-load conditions. Furthermore, the relationship between the softening behavior of surface hardness on the heating pattern and the surface fatigue on the rolling-sliding contact of the developed alloy steels was clarified.

  14. Effect of cyclic outer and inner bending on the fatigue behavior of a multi-layer metal film on a polymer substrate

    Science.gov (United States)

    Kim, Byoung-Joon; Shin, Hae-A.-Seul; Lee, Ji-Hoon; Joo, Young-Chang

    2016-06-01

    The electrical reliability of a multi-layer metal film on a polymer substrate during cyclic inner bending and outer bending is investigated using a bending fatigue system. The electrical resistance of a Cu film on a polymer substrate during cyclic outer bending increases due to fatigue damage formation, such as cracks and extrusion. Cyclic inner bending also leads to fatigue damage and a similar increase in the electrical resistance. In a sample having a NiCr under-layer, however, the electrical resistance increases significantly during outer bending but not during inner bending mode. Cross-sectional observations reveal that brittle cracking in the hard under-layer results in different fatigue behaviors according to the stress mode. By applying an Al over-layer, the fatigue resistance is improved during both outer bending and inner bending by suppressing fatigue damage formation. The effects of the position, materials, and thickness of the inter-layer on the electrical reliability of a multi-layer sample are also investigated. This study can provide meaningful information for designing a multi-layer structure under various mechanical deformations including tensile and compressive stress.

  15. Effect of Notches on Creep-Fatigue Behavior of a P/M Nickel-Based Superalloy

    Science.gov (United States)

    Telesman, Jack; Gabb, Timothy P.; Ghosn, Louis J.; Gayda, John, Jr.

    2015-01-01

    A study was performed to determine and model the effect of high temperature dwells on notched low cycle fatigue (NLCF) and notch stress rupture behavior of a fine grain LSHR powder metallurgy (PM) nickel-based superalloy. It was shown that a 90 second dwell applied at the minimum stress (min dwell) was considerably more detrimental to the NLCF lives than similar dwell applied at the maximum stress (max dwell). The short min dwell NLCF lives were shown to be caused by growth of small oxide blisters which caused preferential cracking when coupled with high concentrated notch root stresses. The cyclic max dwell notch tests failed mostly by a creep accumulation, not by fatigue, with the crack origin shifting internally to a substantial distance away from the notch root. The classical von Mises plastic flow model was unable to match the experimental results while the hydrostatic stress profile generated using the Drucker-Prager plasticity flow model was consistent with the experimental findings. The max dwell NLCF and notch stress rupture tests exhibited substantial creep notch strengthening. The triaxial Bridgman effective stress parameter was able to account for the notch strengthening by collapsing the notched and uniform gage geometry test data into a singular grouping.

  16. Investigation on the fatigue behavior of recycled aggregate concrete under uniaxial compression%再生混凝土单轴受压疲劳性能

    Institute of Scientific and Technical Information of China (English)

    肖建庄; 李宏

    2013-01-01

    The fatigue behavior of recycled aggregate concrete (RAC) with 100% recycled coarse aggregate (RCA) replacement percentage under uniaxial compression loading was tested. Special attentions were devoted to the strain response and damage accumulation of RAC under fatigue loading. The fatigue behavior of RAC was compared with that of natural aggregate concrete ( NAC) in literature. It is found that the old mortar attached to the RCAs, more interfacial transition zones (ITZs) et al. in the RAC have no obvious influence on the fatigue behavior of RAC under uniaxial compression. Based on the analysis of residual strain accumulation, fatigue strain variation, fatigue modulus as well as microcracks propagation, the relationship between the fatigue failure process and the strain response was put forward, and the fatigue damage evolution of RAC was studied. On the basis of the experimental results and continuum damage mechanics, a damage model was proposed for the theoretical and numerical analysis of RAC fatigue behavior.%完成再生粗骨料取代率为100%的再生混凝土单轴受压疲劳试验,着重考察在疲劳荷载作用下的应变响应和疲劳损伤累积.基于文献中普通混凝土受压疲劳性能研究成果,对比分析再生混凝土与普通混凝土的疲劳性能差异,发现再生粗骨料附着老砂浆、再生混凝土中多界面等特点没有引起两种混凝土疲劳性能的显著区别.进一步研究残余应变和疲劳应变的变化情况,并对再生混凝土的疲劳模量与裂纹的扩展进行分析,建立疲劳失效过程与应变响应行为之间的关系,揭示再生混凝土的疲劳损伤演化过程.基于试验结果和连续损伤力学,提出一个再生混凝土损伤模型,可用来对再生混凝土疲劳性能进行理论和数值分析.

  17. Fatigue behavior of Ti–6Al–4V foams processed by magnesium space holder technique

    Energy Technology Data Exchange (ETDEWEB)

    Aşık, E. Erkan, E-mail: eeasik@metu.edu.tr; Bor, Şakir

    2015-01-05

    Porous Ti–6Al–4V alloys are widely used in the biomedical applications for hard tissue implantation due to their elastic moduli being close to that of bone. In this study, porous Ti–6Al–4V alloys were produced with a powder metallurgical process, space holder technique, where magnesium powders were utilized to generate porosity in the range of 51–65 vol%. The production of porous Ti–6Al–4V alloys was composed of three steps. Firstly, spherical Ti–6Al–4V powders with an average size of 55 μm were mixed with spherical magnesium powders, which have been sieved to an average size of 375 μm. Secondly, the mixtures were compacted with a hydraulic press under 500 MPa pressure by using a double-ended steel die. Finally, the green compacts were heated to 1200 °C, during which magnesium powder evaporates, and sintered for 2 h under high purity argon gas atmosphere. Processed foams were investigated under scanning electron microscope and yielded that the foams were composed of spherical, interconnected macropores and irregular shaped micropores. Monotonic compression tests were conducted under quasi-static test conditions to the processed foams. Yield strengths of the foams were found to vary between 69 and 167 MPa and elastic moduli were between 4 and 12 GPa. Processed foams were also dynamically tested under compression–compression fatigue with a stress ratio of 0.1. The foams exhibited similar fatigue response when maximum applied stress was normalized with the average yield strength of the corresponding porosity content. It was found that foams were fatigue immune with a practical limit of 1 million cycles under a maximum applied stress of 0.75σ (normalized)

  18. Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy

    Science.gov (United States)

    Piascik, Robert S.; Newman, John A.

    2002-01-01

    Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.

  19. Fatigue properties of Graphene interconnects on flexible substrates

    Science.gov (United States)

    Paradee, Gary

    This thesis represents the first determination of the fatigue behavior of Graphene as interconnect material electronic components on flexible substrates. The potential application of this interconnect material is for displays on flexible substrates where fatigue resistance is required due to the stress placed on the interconnect during mechanical bending. As the display is cyclically deformed (fatigued) during normal operation, cracks in the interconnect layer initiate and propagate leading to the lineout failure condition. The major contribution of this work is to show that Graphene is a superior interconnect material to the present state of the art Indium Tin Oxide (ITO) due to its electrical, optical and mechanical properties. The experimental approach in this thesis is based on Graphene samples which were fabricated on Silicon Nitrite (Si3N4)/Polyethylene Naphthalate (PEN) substrates. For comparison, both patterned and uniform ITO films ITO films on Si3N4/PEN were fabricated. The results of the in-depth characterization of Graphene are reported and based on Atomic Force Microscopy (AFM), Raman Spectroscopy and Scanning Electron Microscopy (SEM) are reported. The fatigue characteristics of ITO were determined at stress amplitudes ranging from 2000 MPa to 400 MPa up to 5000 cycles. The fatigue characteristics of Graphene were determined at stress amplitudes ranging from 80 GPa to 40 GPa up to 5000 cycles. The fatigue S-N curves were determined and showed that Graphene's endurance limit is 40 GPa. Beyond the endurance limit, there is no observable high cycle or low cycle fatigue indication for Graphene on a flexible substrate such as PEN. The microstructural analysis by SEM and AFM did not reveal normal fatigue crack growth and propagation. This thesis presents the first comprehensive behavior of Graphene in a bending fatigue stress environment present in numerous flexible electronic applications. The design and stress environments for safe operation has been

  20. Fatigue behavior and physical characterization of surface-modified Ti-6Al-4V ELI alloy by micro-arc oxidation

    Directory of Open Access Journals (Sweden)

    Fernanda Potomati

    2012-04-01

    Full Text Available Anodizing has proven an effective method for preparing bioactive titanium and has been the subject of many studies regarding the performance and biological characterization of the layers obtained. However, the fatigue behavior of titanium alloys, after undergoing this process is still poorly studied. This study aims to investigate the influence of MAO (Micro-Arc Oxidation process on the fatigue properties of titanium alloy Ti-6Al-4V. Therefore axial fatigue tests were performed to obtain SxN curves, of specimens in polished and anodized (MAO processed, phosphate salt solution, potential of 290 V conditions. Roughness measurements, SEM, Raman spectra and X-ray photoelectron spectroscopy (XPS analyses were used to characterize the features of the modified surface. SEM was also used to analyze the fatigue fractures of the tested specimens. The MAO process, with the parameters used in this investigation, had no influence on the fatigue behavior of the Ti-6Al-4V alloy, when compared to specimens without surface modification.

  1. Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Barua, Bipul [Argonne National Lab. (ANL), Argonne, IL (United States); Soppet, William K. [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

    2016-09-01

    This report provides an update of an earlier assessment of environmentally assisted fatigue for components in light water reactors. This report is a deliverable in September 2016 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2016 report, we presented a detailed thermal-mechanical stress analysis model for simulating the stress-strain state of a reactor pressure vessel and its nozzles under grid-load-following conditions. In this report, we provide stress-controlled fatigue test data for 508 LAS base metal alloy under different loading amplitudes (constant, variable, and random grid-load-following) and environmental conditions (in air or pressurized water reactor coolant water at 300°C). Also presented is a cyclic plasticity-based analytical model that can simultaneously capture the amplitude and time dependency of the component behavior under fatigue loading. Results related to both amplitude-dependent and amplitude-independent parameters are presented. The validation results for the analytical/mechanistic model are discussed. This report provides guidance for estimating time-dependent, amplitude-independent parameters related to material behavior under different service conditions. The developed mechanistic models and the reported material parameters can be used to conduct more accurate fatigue and ratcheting evaluation of reactor components.

  2. Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti-6Al-4V with and without heat treatment.

    Science.gov (United States)

    Sterling, Amanda J; Torries, Brian; Shamsaei, Nima; Thompson, Scott M

    2016-03-01

    Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti-6Al-4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) - a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their 'as-built', annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti-6Al-4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty.

  3. Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti–6Al–4V with and without heat treatment

    Directory of Open Access Journals (Sweden)

    Amanda J. Sterling

    2016-03-01

    Full Text Available Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti–6Al–4V specimens additively manufactured via Laser Engineered Net Shaping (LENS – a Direct Laser Deposition (DLD process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their ‘as-built’, annealed (below the beta transus temperature, or heat treated (above the beta transus temperature condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti–6Al–4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty.

  4. Fatigue behavior of highly porous titanium produced by powder metallurgy with temporary space holders.

    Science.gov (United States)

    Özbilen, Sedat; Liebert, Daniela; Beck, Tilmann; Bram, Martin

    2016-03-01

    Porous titanium cylinders were produced with a constant amount of temporary space holder (70 vol.%). Different interstitial contents were achieved by varying the starting powders (HDH vs. gas atomized) and manufacturing method (cold compaction without organic binders vs. warm compaction of MIM feedstocks). Interstitial contents (O, C, and N) as a function of manufacturing were measured by chemical analysis. Samples contained 0.34-0.58 wt.% oxygen, which was found to have the greatest effect on mechanical properties. Quasi-static mechanical tests under compression at low strain rate were used for reference and to define parameters for cyclic compression tests. Not unexpectedly, increased oxygen content increased the yield strength of the porous titanium. Cyclic compression fatigue tests were conducted using sinusoidal loading in a servo-hydraulic testing machine. Increased oxygen content was concomitant with embrittlement of the titanium matrix, resulting in significant reduction of compression cycles before failure. For samples with 0.34 wt.% oxygen, R, σ(min) and σ(max) were varied systematically to estimate the fatigue limit (~4 million cycles). Microstructural changes induced by cyclic loading were then characterized by optical microscopy, SEM and EBSD.

  5. Structural integrity of additive materials: Microstructure, fatigue behavior, and surface processing

    Science.gov (United States)

    Book, Todd A.

    Although Additive Manufacturing (AM) offers numerous performance advantages over existing methods, AM structures are not being utilized for critical aerospace and mechanical applications due to uncertainties in their structural integrity as a result of the microstructural variations and defects arising from the AM process itself. Two of these uncertainties are the observed scatter in tensile strength and fatigue lives of direct metal laser sintering (DMLS) parts. With strain localization a precursor for material failure, this research seeks to explore the impact of microstructural variations in DMLS produced materials on strain localization. The first part of this research explores the role of the microstructure in strain localization of DMLS produced IN718 and Ti6Al4V specimens (as-built and post-processed) through the characterization of the linkage between microstructural variations, and the accumulation of plastic strain during monotonic and low cycle fatigue loading. The second part of this research explores the feasibility for the application of select surface processing techniques in-situ during the DMLS build process to alter the microstructure in AlSi10Mg to reduce strain localization and improve material cohesion. This study is based on utilizing experimental observations through the employment of advanced material characterization techniques such as digital image correlation to illustrate the impacts of DMLS microstructural variation.

  6. Effect of W and Ta on creep–fatigue interaction behavior of reduced activation ferritic–martensitic (RAFM) steels

    Energy Technology Data Exchange (ETDEWEB)

    Shankar, Vani, E-mail: vani@igcar.gov.in [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Institute for Plasma Research, Ahmedabad 382428 (India); Mariappan, K.; Sandhya, R.; Laha, K.; Jayakumar, T.; Kumar, E. Rajendra [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Institute for Plasma Research, Ahmedabad 382428 (India)

    2015-11-15

    Highlights: • SR correlated with deformation under CFI in RAFM steels. • Stress relaxation directly related to plastic strain accumulated, inversely to CFI life. • Optimum combination of W and Ta best for CFI life. • RAFM steels demonstrated compressive dwell sensitivity. • SR tends toward constant value at long hold. - Abstract: The aim of this work is to understand the effect of varying tungsten and tantalum contents on creep–fatigue interaction (CFI) behavior of reduced activation ferritic–martensitic (RAFM) steels. Increase in W improved CFI life. Effect of changing Ta and W upon the resultant CFI life seems to be interrelated and an optimum combination of both W and Ta works out to be the best for CFI life. Stress relaxation obtained during application of hold can be a useful parameter to relate deformation and damage in the RAFM steels.

  7. Influence of Al on the fatigue crack growth behavior of Fe–22Mn–(3Al)–0.6C TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Penghui [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China); Qian, Lihe, E-mail: dlhqian@yahoo.com [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China); Meng, Jiangying [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Liu, Shuai; Zhang, Fucheng [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China)

    2015-10-01

    The influence of Al on fatigue crack growth (FCG) behavior of the high-Mn austenitic twinning-induced plasticity (TWIP) steel was investigated by conducting FCG tests on Fe–22Mn–0Al–0.6C and Fe–22Mn–3Al–0.6C TWIP steels (hereafter, referred to as 0Al and 3Al TWIP steel, respectively). The FCG tests were performed at stress ratio of 0.1 under the control of stress intensity factor range using three-point bending specimens. Excepting that the traditional two-dimensional (2D) observation methods (optical, scanning and transmission electron microscopes) were used to observe the crack paths, fracture surfaces and microstructure features, a high-resolution synchrotron X-ray computed tomography was also applied to observe the three-dimensional (3-D) crack morphology. The results indicate that the FCG resistance of the 0Al TWIP steel is superior to that of 3Al TWIP steel in the near threshold regime. Observed from the 2D crack paths and 3D crack morphologies, it can be found that the crack surface roughness and crack deflection of the 0Al steel are greater than those of 3Al steel. It is suggested that the degree of roughness-induced crack closure decreases with the addition of Al. And the 0Al steel shows much larger plastic zone sizes ahead of the crack tip than the 3Al steel, suggesting that plasticity-induced crack closure may also play an important role in decreasing the FCG rate in the 0Al steel. By excluding the crack closure effects, the 0Al steel still exhibits a higher effective crack growth threshold value than the 3Al steel; this is considered to be due to the higher planarity of slip in the 0Al steel than in the 3Al steel, and the mechanical twins generated in the 0Al steel reduce the stress concentration at crack tip.

  8. Honey bee lines selected for high propolis production also have superior hygienic behavior and increased honey and pollen stores.

    Science.gov (United States)

    Nicodemo, D; De Jong, D; Couto, R H N; Malheiros, E B

    2013-12-19

    Honey bees use propolis to defend against invaders and disease organisms. As some colonies produce much more propolis than others, we investigated whether propolis collecting is associated with disease resistance traits, including hygienic behavior and resistance to the parasitic bee mite, Varroa destructor. The three highest (HP) and three lowest propolis-producing (LP) colonies among 36 Africanized honey bee colonies were initially selected. Queens and drones from these colonies were crossed through artificial insemination to produce five colonies of each of the following crosses: HP♀ X HP♂, LP♀ X HP♂, HP♀ X LP♂, and LP♀ X LP♂. Colonies headed by HP♀ X HP♂ queens produced significantly more propolis than those with HP♀ X LP♂ and LP♀ X HP♂ queens and these in turn produced significantly more propolis than those headed by LP♀ X LP♂ queens. The brood cell uncapping rate of the high-propolis-producing colonies in the hygienic behavior test was significantly superior to that of the other groups. The LP X LP group was significantly less hygienic than the two HP X LP crosses, based on the evaluation of the rate of removal of pin-killed pupae. The HP X HP colonies were significantly more hygienic than the other crosses. No significant differences were found in mite infestation rates among the groups of colonies; although overall, colony infestation rates were quite low (1.0 to 3.2 mites per 100 brood cells), which could have masked such effects. Honey and pollen stores were significantly and positively correlated with propolis production.

  9. Evaluation of an mHealth intervention aiming to improve health-related behavior and sleep and reduce fatigue among airline pilots.

    Science.gov (United States)

    van Drongelen, Alwin; Boot, Cécile Rl; Hlobil, Hynek; Twisk, Jos Wr; Smid, Tjabe; van der Beek, Allard J

    2014-11-01

    The aim of this study was to evaluate the effects of an mHealth intervention (intervention using mobile technology) consisting of tailored advice regarding exposure to daylight, sleep, physical activity, and nutrition, and aiming to improve health-related behavior, thereby reducing sleep problems and fatigue and improving health perception of airline pilots. A randomized controlled trial was conducted among 502 airline pilots. The intervention group was given access to both the MORE Energy mobile application (app) with tailored advice and a website with background information. The control group was directed to a website with standard information about fatigue. Health-related behavior, fatigue, sleep, and health perception outcomes were measured through online questionnaires at baseline and at three and six months after baseline. The effectiveness of the intervention was determined using linear and Poisson mixed model analyses. After six months, compared to the control group, the intervention group showed a significant improvement on fatigue (β= -3.76, P<0.001), sleep quality (β= -0.59, P=0.007), strenuous physical activity (β=0.17, P=0.028), and snacking behavior (β= -0.81, P<0.001). No significant effects were found for other outcome measures. The MORE Energy mHealth intervention reduced self-reported fatigue compared to a minimal intervention. Some aspects of health-related behavior (physical activity and snacking behavior) and sleep (sleep quality) improved as well, but most did not. The results show offering tailored advice through an mHealth intervention is an effective means to support employees who have to cope with irregular flight schedules and circadian disruption. This kind of intervention might therefore also be beneficial for other working populations with irregular working hours.

  10. Effects of Relaxing Music on Mental Fatigue Induced by a Continuous Performance Task: Behavioral and ERPs Evidence.

    Directory of Open Access Journals (Sweden)

    Wei Guo

    Full Text Available The purpose of this study was to investigate whether listening to relaxing music would help reduce mental fatigue and to maintain performance after a continuous performance task. The experiment involved two fatigue evaluation phases carried out before and after a fatigue inducing phase. A 1-hour AX-continuous performance test was used to induce mental fatigue in the fatigue-inducing phase, and participants' subjective evaluation on the mental fatigue, as well as their neurobehavioral performance in a Go/NoGo task, were measured before and after the fatigue-inducing phase. A total of 36 undergraduate students (18-22 years participated in the study and were randomly assigned to the music group and control group. The music group performed the fatigue-inducing task while listening to relaxing music, and the control group performed the same task without any music. Our results revealed that after the fatigue-inducing phase, (a the music group demonstrated significantly less mental fatigue than control group, (b reaction time significantly increased for the control group but not for the music group, (c larger Go-P3 and NoGo-P3 amplitudes were observed in the music group, although larger NoGo-N2 amplitudes were detected for both groups. These results combined to suggest that listening to relaxing music alleviated the mental fatigue associated with performing an enduring cognitive-motor task.

  11. Effects of Relaxing Music on Mental Fatigue Induced by a Continuous Performance Task: Behavioral and ERPs Evidence.

    Science.gov (United States)

    Guo, Wei; Ren, Jie; Wang, Biye; Zhu, Qin

    2015-01-01

    The purpose of this study was to investigate whether listening to relaxing music would help reduce mental fatigue and to maintain performance after a continuous performance task. The experiment involved two fatigue evaluation phases carried out before and after a fatigue inducing phase. A 1-hour AX-continuous performance test was used to induce mental fatigue in the fatigue-inducing phase, and participants' subjective evaluation on the mental fatigue, as well as their neurobehavioral performance in a Go/NoGo task, were measured before and after the fatigue-inducing phase. A total of 36 undergraduate students (18-22 years) participated in the study and were randomly assigned to the music group and control group. The music group performed the fatigue-inducing task while listening to relaxing music, and the control group performed the same task without any music. Our results revealed that after the fatigue-inducing phase, (a) the music group demonstrated significantly less mental fatigue than control group, (b) reaction time significantly increased for the control group but not for the music group, (c) larger Go-P3 and NoGo-P3 amplitudes were observed in the music group, although larger NoGo-N2 amplitudes were detected for both groups. These results combined to suggest that listening to relaxing music alleviated the mental fatigue associated with performing an enduring cognitive-motor task.

  12. Data demonstrating the effects of build orientation and heat treatment on fatigue behavior of selective laser melted 17–4 PH stainless steel

    Directory of Open Access Journals (Sweden)

    Aref Yadollahi

    2016-06-01

    Full Text Available Axial fully-reversed strain-controlled (R=−1 fatigue experiments were performed to obtain data demonstrating the effects of building orientation (i.e. vertical versus horizontal and heat treatment on the fatigue behavior of 17–4 PH stainless steel (SS fabricated via Selective Laser Melting (SLM (Yadollahi et al., submitted for publication [1]. This data article provides detailed experimental data including cyclic stress-strain responses, variations of peak stresses during cyclic deformation, and fractography of post-mortem specimens for SLM 17–4 PH SS.

  13. Data demonstrating the effects of build orientation and heat treatment on fatigue behavior of selective laser melted 17-4 PH stainless steel.

    Science.gov (United States)

    Yadollahi, Aref; Simsiriwong, Jutima; Thompson, Scott M; Shamsaei, Nima

    2016-06-01

    Axial fully-reversed strain-controlled ([Formula: see text]) fatigue experiments were performed to obtain data demonstrating the effects of building orientation (i.e. vertical versus horizontal) and heat treatment on the fatigue behavior of 17-4 PH stainless steel (SS) fabricated via Selective Laser Melting (SLM) (Yadollahi et al., submitted for publication [1]). This data article provides detailed experimental data including cyclic stress-strain responses, variations of peak stresses during cyclic deformation, and fractography of post-mortem specimens for SLM 17-4 PH SS.

  14. Effect of temperature, microstructure, and stress state on the low cycle fatigue behavior of Waspaloy

    Science.gov (United States)

    Stahl, D. R.; Antolovich, S. D.; Mirdamadi, M.; Zamrik, S. Y.

    1988-01-01

    Specimens of Waspaloy of two different microstructures were tested in uniaxial and torsional low-cycle fatigue at 24 and 649 C. For all specimens, deformation and failure mechanisms are found to be independent of stress state at 24 C; in both microstructures, failure is associated with the formation of shear cracks. At 649 C, deformation and failure mechanisms for the fine-grain large gamma-prime specimens are independent of stress state, and the mechanisms are similar to those observed at 24 C. For the coarse-grain small gamma-prime specimens, however, failure occurs on principal planes in torsion and on shear plane in uniaxial tension. The results are interpreted in terms of deformation mode and microstructural instability.

  15. Study of creep-fatigue behavior in a 1000 MW rotor using a phenomenological lifetime model

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Nailong; Wang, Weizhe; Jiang, Jishen; Liu, Yingzheng [School of Mechanical Engineering, Shanghai (China)

    2017-02-15

    In this study, the phenomenological lifetime model was applied to part of an ultra-supercritical steam turbine rotor model to predict its lifetime as a post processing of the finite element method. To validate the accuracy and adaptation of the post processing program, stress strain hysteresis loops of a cylinderal model under service-like load cycle conditions in cycle N = 1 and 300 were constructed, and the comparison of the results with experimental data on the same cylinderal specimen showed them to be satisfactory. The temperature and von Mises stress distributions of the rotor during a startup-running-shutdown-natural cool process were numerically studied using ABAQUS and the damage caused by the interaction of creep and fatigue was subsequently computed and discussed. It was found that the maximum damage appeared at the inlet notch zone, with the blade groove areas and the front notch areas also suffering a large damage amplitude.

  16. Fatigue behavior of GMAW welded Aluminium alloy AA7020; Comportamiento a fatiga de uniones soldadas GMAW de la aleacion de aluminio AA 7020

    Energy Technology Data Exchange (ETDEWEB)

    Bloem, C. A.; Salvador, M. D.; Amigo, V.; Vicente, A.

    2007-07-01

    The aim of this investigation is to evaluate the influence on the fatigue behavior by the finishing of the bulge in a welded aluminium-zinc-magnesium alloy AA7020. It was determined that total or partial elimination of the bulge has very little influence on its behavior, giving a very similar result on both cases, where one is better than the other by only 3%. (Author) 20 refs.

  17. Fatigue behavior of thin-walled grade 2 titanium samples processed by selective laser melting. Application to life prediction of porous titanium implants.

    Science.gov (United States)

    Lipinski, P; Barbas, A; Bonnet, A-S

    2013-12-01

    Because of its biocompatibility and high mechanical properties, the commercially pure grade 2 titanium (CPG2Ti) is largely used for fabrication of patient specific implants or hard tissue substitutes with complex shape. To avoid the stress-shielding and help their colonization by bone, prostheses with a controlled porosity are designed. The selective laser melting (SLM) is well adapted to manufacture such geometrically complicated structures constituted by struts with rough surfaces and relatively small diameters. Few studies were dedicated to characterize the fatigue properties of SLM processed samples and bulk parts. They followed conventional or standard protocols. The fatigue behavior of standard samples is very different from the one of porous raw structures. In this study, the SLM made "as built" (AB) and "heat treated" (HT) tubular samples were tested in fatigue. Wöhler curves were determined in both cases. The obtained endurance limits were equal to σD(AB)=74.5MPa and σD(HT)=65.7MPa, respectively. The heat treatment worsened the endurance limit by relaxation of negative residual stresses measured on the external surface of the samples. Modified Goodman diagram was established for raw specimens. Porous samples, based on the pattern developed by Barbas et al. (2012), were manufactured by SLM. Fatigue tests and finite element simulations performed on these samples enabled the determination of a simple rule of fatigue assessment. The method based on the stress gradient appeared as the best approach to take into account the notch influence on the fatigue life of CPG2Ti structures with a controlled porosity. The direction dependent apparent fatigue strength was found. A criterion based on the effective, or global, nominal stress was proposed taking into account the anisotropy of the porous structures. Thanks to this criterion, the usual calculation methods can be used to design bone substitutes, without a precise modelling of their internal fine porosity.

  18. The effect of post-sintering treatments on the fatigue and biological behavior of Ti-6Al-4V ELI parts made by selective laser melting.

    Science.gov (United States)

    Benedetti, M; Torresani, E; Leoni, M; Fontanari, V; Bandini, M; Pederzolli, C; Potrich, C

    2017-03-28

    Fatigue resistance and biocompatibility are key parameters for the successful implantation of hard-tissue prostheses, which nowadays are more and more frequently manufactured by selective laser melting (SLM). For this purpose, the present paper is aimed at investigating the effect of post-sintering treatments on the fatigue behavior and biological properties of Ti samples produced by SLM. After the building process, all samples are heat treated to achieve a complete stress relief. The remaining ones are tribofinished with the aim of reducing the surface roughness of the as-sintered condition. Part of the tribofinished samples are then subjected to one of the following post-sintering treatments: (i) shot peening, (ii) hot isostatic pressing (HIP), and (iii) electropolishing. It is found that shot peening and HIP are the most effective treatments to improve the high and the very-high cycle fatigue resistance, respectively. At the same time, they preserve the good biocompatibility ensured by the biomedical Titanium Grade 23.

  19. Fatigue crack growth behaviors of SA508 Gr.3 Cl.2 base and weld material in 290 .deg. C water environment

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Pyungyeon; Kim, Jeong Hyeon; Jang, Changheui [KAIST, Daejeon (Korea, Republic of); Cho, Hyunchul [Doosan Heavy Industries and Construction Co., Ltd., Changwon (Korea, Republic of)

    2012-04-15

    The fatigue crack growth behaviors of SA508 Gr.3 Cl.2 low alloy steel in high temperature water environment were investigated. Overall, weld metal showed similar crack growth rate as that of base metal. At 0.01 Hz, fatigue crack growth rate (FCGR) was higher than that in air while the difference was smaller at 0.1 Hz. Also, FCGR showed ΔK dependency at 0.1 Hz only, indicating that the environmental effect was much greater at slower loading frequency of 0.01 Hz. FCGR of SA508 Gr.3 Cl.2 low alloy steel was compatible to or smaller than the ASME Sec. XI fatigue reference curves in high temperature water environment.

  20. Mechanical behavior of materials engineering methods for deformation, fracture, and fatigue

    CERN Document Server

    Dowling, Norman E

    2012-01-01

    For upper-level undergraduate engineering courses in Mechanical Behavior of Materials. Mechanical Behavior of Materials, 4/e introduces the spectrum of mechanical behavior of materials, emphasizing practical engineering methods for testing structural materials to obtain their properties, and predicting their strength and life when used for machines, vehicles, and structures. With its logical treatment and ready-to-use format, it is ideal for upper-level undergraduate students who have completed elementary mechanics of materials courses.

  1. The influence of silicon and aluminum on austenite deformation behavior during fatigue and tensile loading

    Science.gov (United States)

    Lehnhoff, Gregory R.

    Advanced high strength steels (AHSS) for automobile light-weighting utilize Si and Al alloying to retain austenite in the microstructure during thermal partitioning treatments. This research project utilized fully austenitic steels with varied Si and Al compositions to understand the effect of these elements on austenite deformation response, including deformation induced martensite formation and deformation twinning. Specific focus was directed at understanding austenite deformation response during fatigue loading. Independent alloying additions of 2.5 wt pct Si and Al were made to a base steel composition of 15 Ni - 11 Cr - 1 Mn - 0.03 C (wt pct). Weak beam dark field transmission electron microscopy (TEM) imaging of dissociated dislocations was implemented to experimentally determine the influences of Si and Al on austenite stacking fault energy (SFE). The 2.5 wt pct Si alloying addition decreased the SFE by 6.4 mJ/m2, while the 2.5 wt pct Al alloying increased the SFE by 12 mJ/m2. Fully reversed, total strain controlled, low cycle fatigue (LCF) tests indicated that all four alloys underwent primary cyclic hardening and stabilization. Secondary cyclic strain hardening was correlated to BCC martensite formation using Feritscope magnetic fraction measurements of LCF specimens; the formation of 1 pct martensite led to 7 MPa of secondary hardening. TEM showed that martensite predominantly formed as parallel, irregular bands through strain induced nucleation on austenite shear bands. The austenite shear bands consisted of austenite {111} planes with concentrated dislocations, stacking faults, and/or HCP epsilon-martensite. Aluminum alloying promoted martensite formation during LCF, while Si suppressed martensite. Therefore, the strain induced nucleation process was not suppressed by the increased SFE associated with Al alloying. Tensile testing indicated that Si alloying promoted deformation twinning by lowering the SFE. Similarly to LCF loading, Al promoted

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  3. Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel

    Science.gov (United States)

    Kumar, Jalaj; Ahmad, S.; Mukhopadhyay, C. K.; Jayakumar, T.; Kumar, Vikas

    2016-01-01

    High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.

  4. Microstructure vs. Near-threshold Fatigue Crack Growth Behavior of an Heat-treated Ductile Iron

    Directory of Open Access Journals (Sweden)

    Radomila KONEČNÁ

    2012-03-01

    Full Text Available Perferritic isothermal ductile iron (IDI® is an intermediate grade between the low-strength grades of austempered ductile iron (ADI and pearlitic ductile iron (DI recently developed by Zanardi Fonderie Italy. IDI is produced by heat-treating an unalloyed nodular cast iron. The specific matrix microstructure is called “Perferritic” and consists predominantly of ferrite and pearlite. Compared to the pearlitic grades of nodular ductile iron, IDI combines similar strength with higher toughness as a result of the isothermal heat treatment. In this contribution the fatigue crack growth resistance and Kath of IDI are investigated and correlated to mechanical properties and microstructural features. The threshold Ka was determined using the load shedding technique as per ASTM Standard E-647 using CT specimens extracted from a cast block. Tensile specimens were extracted from the broken CT halves and used to determine the static mechanical properties. A metallographic investigation was carried out to correlate structural features and mechanical properties.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1336

  5. Cognitive behavioral therapy for insomnia comorbid with COPD is feasible with preliminary evidence of positive sleep and fatigue effects.

    Science.gov (United States)

    Kapella, Mary C; Herdegen, James J; Perlis, Michael L; Shaver, Joan L; Larson, Janet L; Law, Julie A; Carley, David W

    2011-01-01

    Many people with COPD report difficulties falling asleep or staying asleep, insufficient sleep duration, or nonrestorative sleep. Cognitive behavioral therapy for insomnia (CBT-I) has proved effective not only in people with primary insomnia but also in people with insomnia comorbid with psychiatric and medical illness (eg, depression, cancer, and chronic pain). However, CBT-I has rarely been tested in those with COPD who have disease-related features that interfere with sleep and may lessen the effectiveness of such therapies. The purpose of this study was to determine the feasibility of applying a CBT-I intervention for people with COPD and to assess the impact of CBT-I on insomnia severity and sleep-related outcomes, fatigue, mood, and daytime functioning. The study had two phases. In Phase 1, a 6-weekly session CBT-I intervention protocol in participants with COPD was assessed to examine feasibility and acceptability. Phase 2 was a small trial utilizing a prospective two-group pre- and post-test design with random assignment to the six-session CBT-I or a six-session wellness education (WE) program to determine the effects of each intervention, with both interventions being provided by a nurse behavioral sleep medicine specialist. Fourteen participants (five in Phase 1 and nine in Phase 2) completed six sessions of CBT-I and nine participants completed six sessions of WE. Participants indicated that both interventions were acceptable. Significant positive treatment-related effects of the CBT-I intervention were noted for insomnia severity (P = 0.000), global sleep quality (P = 0.002), wake after sleep onset (P = 0.03), sleep efficiency (P = 0.02), fatigue (P = 0.005), and beliefs and attitudes about sleep (P = 0.000). Significant positive effects were noted for depressed mood after WE (P = 0.005). Results suggest that using CBT-I in COPD is feasible and the outcomes compare favorably with those obtained in older adults with insomnia in the context of other

  6. "Shifts in attention during mental fatigue: Evidence from subjective, behavioral, physiological, and eye-tracking data": Correction to Hopstaken et al. (2016).

    Science.gov (United States)

    2016-09-01

    Reports an error in "Shifts in attention during mental fatigue: Evidence from subjective, behavioral, physiological, and eye-tracking data" by Jesper F. Hopstaken, Dimitri van der Linden, Arnold B. Bakker, Michiel A. J. Kompier and Yik Kiu Leung (Journal of Experimental Psychology: Human Perception and Performance, 2016[Jun], Vol 42[6], 878-889). In the article, there were formatting errors in columns 1 through 8 of Table 2. The correct table is present in the erratum. (The following abstract of the original article appeared in record 2016-01220-001.) There is an increasing amount of evidence that during mental fatigue, shifts in motivation drive performance rather than reductions in finite mental energy. So far, studies that investigated such an approach have mainly focused on cognitive indicators of task engagement that were measured during controlled tasks, offering limited to no alternative stimuli. Therefore it remained unclear whether during fatigue, attention is diverted to stimuli that are unrelated to the task, or whether fatigued individuals still focused on the task but were unable to use their cognitive resources efficiently. With a combination of subjective, EEG, pupil, eye-tracking, and performance measures the present study investigated the influence of mental fatigue on a cognitive task which also contained alternative task-unrelated stimuli. With increasing time-on-task, task engagement and performance decreased, but there was no significant decrease in gaze toward the task-related stimuli. After increasing the task rewards, irrelevant rewarding stimuli where largely ignored, and task engagement and performance were restored, even though participants still reported to be highly fatigued. Overall, these findings support an explanation of less efficient processing of the task that is influenced by motivational cost/reward tradeoffs, rather than a depletion of a finite mental energy resource. PsycINFO Database Record (c) 2016 APA, all rights reserved

  7. Rotary bending fatigue behavior of A356 –T6 aluminum alloys by vacuum pressurizing casting

    Directory of Open Access Journals (Sweden)

    Yong-qin Liu

    2015-09-01

    Full Text Available Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.

  8. Microstructural characterization of the chemomechanical behavior of asphalt in terms of aging and fatigue performance properties

    Science.gov (United States)

    Allen, Robert Grover

    The study of asphalt chemo-mechanics requires a basic understanding of the physical properties and chemical composition of asphalt and how these properties are linked to changes in performance induced by chemical modifications. This work uniquely implements the framework of chemo-mechanics by investigating two types of chemical modification processes, natural (oxidative aging) and synthetic (chemical doping) as they relate not only to macro-scale properties of asphalt binder but also to the asphalt microstructure and nanorheology. Furthermore, this study demonstrates the application of atomic force microscopy (AFM) imaging and the extraction of nano-scale engineering properties, i.e. elastic modulus, relaxation modulus, and surface energy, as a method to predict performance related to the fatigue characteristics of asphalt binders by modeling intrinsic material flaws present amongst phase interfaces. It was revealed that oxidative aging induces substantial microstructural changes in asphalt, including variations in phase structure, phase properties, and phase distribution. It has also been shown that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. In fact, particular phases that emerged via chemical doping revealed a surprising correlation between oxidative aging and the saturates chemical parameter of asphalt in terms of how they explicitly impact durability and performance of asphalt. By implementing a crack initiation model---which requires measureable microstructural characteristics as an input parameter---it was found that microstructural flaws (depending on the extremity) can have a more profound impact on asphalt performance than the properties of the material located between the flaws. It was also discovered by comparing the findings to performance data in the Strategic Highway Research Program's (SHRP's) Materials Reference Library (MRL), that the crack initiation model

  9. Fatigue crack micromechanisms in a Cu-Zn-Al shape memory alloy with pseudo-elastic behavior

    Directory of Open Access Journals (Sweden)

    Vittorio Di Cocco

    2015-10-01

    Full Text Available Shape memory property characterizes the behavior of many Ti based and Cu based alloys (SMAs. In Cu-Zn-Al SMAs, the original shape recovering is due to a bcc phase that is stable at high temperature. After an appropriate cooling process, this phase (β-phase or austenitic phase transforms reversibly into a B2 structure (transition phase and, after a further cooling process or a plastic deformation, it transforms into a DO3 phase (martensitic phase. In β-Cu-Zn-Al SMAs, the martensitic transformation due to plastic deformation is not stable at room temperature: a high temperature “austenitization” process followed by a high speed cooling process allow to obtain a martensitic phase with a higher stability. In this work, a Cu-Zn-Al SMA in “as cast” conditions has been microstructurally and metallographically characterized by means of X-Ray diffraction and Light Optical Microscope (LOM observations. Fatigue crack propagation resistance and damaging micromechanisms have been investigated corresponding to three different load ratios (R=0.10, 0.50 and 0.75

  10. Fatigue and corrosion fatigue behavior of 13Cr and duplex stainless steel and a welded nickel alloy employed in oil and gas production

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, R.M. [Department of Metallurgy Engineering, Federal University of Rio Grande do Sul, Porto Alegre (Brazil); Juca Batista, Ipanema, Porto Alegre, Rio Grande do Sul CEP (Brazil); Mueller, I.L. [Department of Metallurgy Engineering, Federal University of Rio Grande do Sul, Porto Alegre (Brazil); Aneron Correia de Oliveira, Porto Alegre, Rio Grande do Sul (Brazil)

    2009-05-15

    The materials used in off-shore oil and gas production, e.g. in risers, are often exposed to cyclic loads from the water movement because of their contact with seawater. These factors acting together can develop a corrosion fatigue (CF) process. A duplex and a 13% chromium (13Cr) wrought stainless steel (SS) and a welded nickel base alloy Inconel 625 were tested at different cyclic load magnitudes in an eccentric fatigue machine type. The specimens were tested in the presence of a corrosive environment at low loading frequencies (0.3 Hz). The medium used was an aqueous solution with 115.000 ppm of chloride, pH adjusted to 4, and CO{sub 2} bubbling inside the solution during the test. The end of the test was determined in maximum 500.000 cycles (23 days for frequency of 0.3 Hz) if no fracture occurred before. In the 13Cr steel the fissure seems to propagate in a uniform unique path, while in the duplex steel the crack changes the direction when passing from the ferritic to austenitic grains. The propagation speed seems to be different in the ferrite and in the austenitic structures. Among the materials tested the Inconel 625 alloy, even being in the welded condition, showed higher CF strength than the SSs; 13Cr shows better results when compared with the duplex steel, even though the last one would be more corrosion resistant. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  11. The Analysis of Fatigue Behavior of Joint-strengthened Component in Aircraft%飞机连接加强件疲劳特性分析

    Institute of Scientific and Technical Information of China (English)

    何宇廷; 富贵华

    2001-01-01

    To analyze the fatigue behavior of joint-strengthened component in aircraft, a series of special finite element method (FEM) programs, in which 4-node isoparametric plane elements and two-dimensional rivet elements are used, are presented to analyze the detail stresses of the riveted component. After calculating the detail stresses of joint-strengthened component and determining its fatigue dangerous position, the stress severity factor method is used to calculate the fatigue life of the component and its fatigue safety life is gained.%针对飞机上一重要承力连接加强件,采用平 面四节点等参元与二维受剪钉元组合而成的有限元程序进行了细节应力分析,确定了疲劳危 险部位。接着,在给定的等效载荷谱作用下,采用应力严重系数法计算了其疲劳寿命,得到 了有益的结果。

  12. Effect of specimen thickness of fatigue-crack-growth behavior and fracture toughness of 7075-T6 and 7178-T6 aluminum alloys

    Science.gov (United States)

    Hudson, C. M.; Newman, J. C., Jr.

    1973-01-01

    A study was made to determine the effects of specimen thickness on fatigue crack growth and fracture behavior of 7075-T6 and 7178-T6 aluminum alloy sheet and plate. Specimen thicknesses ranged from 5.1 to 12.7 mm (0.20 to 0.50 in.) for 7075-T6 and from 1.3 to 6.4 mm (0.05 to 0.25 in.) for 7178-T6. The stress ratios R used in the crack growth experiments were 0.02 and 0.50. For 7075-T6, specimen thickness had relatively little effect on fatigue-crack growth. However, the fracture toughness of the thickness of the thickest gage of 7075-T6 was about two-thirds of the fracture toughness of the thinner gages of 7075-T6. For 7178-T6, fatigue cracks generally grew somewhat faster in the thicker gages than in the thinnest gage. The fracture toughness of the thickest gage of 7178-T6 was about two-thirds of the fracture toughness of the thinner gages of 7178-T6. Stress intensity methods were used to analyze the experimental results. For a given thickness and value of R, the rate of fatigue crack growth was essentially a single-valued function of the stress intensity range for 7075-T6 and 7178-T6. An empirical equation developed by Forman, Kearney, and Engle fit the 7075-T6 and 7178-T6 crack growth data reasonably well.

  13. Three-dimensional fatigue crack growth behavior in an aluminum alloy investigated with in situ high-resolution synchrotron X-ray microtomography

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H., E-mail: huizhang@sp-mac4.pse.tut.ac.jp [Department of Production Systems Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580 (Japan); Toda, H.; Qu, P.C.; Sakaguchi, Y.; Kobayashi, M. [Department of Production Systems Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tempaku, Toyohashi, Aichi 441-8580 (Japan); Uesugi, K.; Suzuki, Y. [Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198 (Japan)

    2009-06-15

    The fatigue crack propagation process in an Al-Mg-Si alloy was investigated using in situ high-resolution synchrotron radiation X-ray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120,000 fatigue cycles. Three-dimensional rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and closure levels was discussed and interpreted.

  14. Mechanical Behavior of Lithium-Ion Batteries and Fatigue Behavior of Ultrasonic Weld-Bonded Lap-Shear Specimens of Dissimilar Magnesium and Steel Sheets

    Science.gov (United States)

    Lai, Wei-Jen

    The mechanical behaviors of LiFePO4 battery cell and module specimens under in-plane constrained compression were investigated for simulations of battery cells, modules and packs under crush conditions. The experimental stress-strain curves were correlated to the deformation patterns of battery cell and module specimens. Analytical solutions were developed to estimate the buckling stresses and to provide a theoretical basis for future design of representative volume element cell and module specimens. A physical kinematics model for formation of kinks and shear bands in battery cells was developed to explain the deformation mechanism for layered battery cells under in-plane constrained compression. A small-scale module constrained punch indentation test was also conducted to benchmark the computational results. The computational results indicate that macro homogenized material models can be used to simulate battery modules under crush conditions. Fatigue behavior and failure modes of ultrasonic spot welds in lap-shear specimens of magnesium and steel sheets with and without adhesive were investigated. For ultrasonic spot welded lap-shear specimens, the failure mode changes from the partial nugget pullout mode under low-cycle loading conditions to the kinked crack failure mode under high-cycle loading conditions. For adhesive-bonded and weld-bonded lap-shear specimens, the test results show the near interface cohesive failure mode and the kinked crack failure mode under low-cycle and high-cycle loading conditions, respectively. Next, the analytical effective stress intensity factor solutions for main cracks in lap-shear specimens of three dissimilar sheets under plane strain conditions were developed and the solutions agreed well with the computational results. The analytical effective stress intensity factor solutions for kinked cracks were compared with the computational results at small kink lengths. The results indicate that the computational results approach to

  15. Effects of warm laser peening at elevated temperature on the low-cycle fatigue behavior of Ti6Al4V alloy

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J.Z.; Meng, X.K., E-mail: mengdetiankong10@126.com; Huang, S.; Sheng, J.; Lu, J.Z.; Yang, Z.R.; Su, C.

    2015-09-03

    This study focused on the effects of warm laser peening (WLP) on the fatigue behavior of Ti6Al4V titanium alloy during low-cycle fatigue (LCF) tests. The Ti6Al4V specimens were treated by laser peening at room temperature (RT-LP) and WLP at elevated temperatures from 100 °C to 400 °C. The residual stress relaxation (RSR) tests and LCF tests were conducted subsequently. In addition, the microstructure analysis of fracture surfaces was performed using scanning electron microscope (SEM). Finally, the fracture mechanism of the untreated, RT-LPed and 300 °C-WLPed samples during LCF was revealed. It is found that although the compressive residual stress (CRS) induced by WLP decreases at elevated temperatures, the depth and stability of CRS increase with the increasing treatment temperature, which help to retard the early fatigue crack initiation. Moreover, for the 300 °C-WLPed specimens, the growth rate of effective cracks is decreased and the lengths of crack growth paths are increased by the induced high angle boundaries (HABs) and nano-precipitates. Therefore, specimens treated by WLP at 300 °C are found to have a significantly extended fatigue life when subjected to low-cycle loads. This extended fatigue life is attributed to the great depth and stability of introduced CRS, as well as the enhanced fracture toughness. It can be concluded that 300 °C is the optimal temperature for WLP of Ti6Al4V titanium alloy from the perspective of LCF improvement.

  16. Fatigue Crack Growth Behavior of Nickel-base Superalloy Haynes 282 at 550-750 °C

    Science.gov (United States)

    Rozman, K. A.; Kruzic, J. J.; Hawk, J. A.

    2015-08-01

    The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at temperatures of 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 Hz and 0.25 Hz. Increasing the temperature from 550 to 750 °C caused the fatigue crack growth rates to increase from ~20 to 60% depending upon the applied stress intensity level. The effect of reducing the applied loading frequency increased the fatigue crack growth rates from ~20 to 70%, also depending upon the applied stress intensity range. The crack path was observed to be transgranular for the temperatures and frequencies used during fatigue crack growth rate testing. At 750 °C, there were some indications of limited intergranular cracking excursions at both loading frequencies; however, the extent of intergranular crack growth was limited and the cause is not understood at this time.

  17. Nociceptive behaviors were induced by electrical stimulation of the dura mater surrounding the superior sagittal sinus in conscious adult rats and reduced by morphine and rizatriptan benzoate.

    Science.gov (United States)

    Dong, Zhao; Jiang, Lei; Wang, Xiaohui; Wang, Xiaolin; Yu, Shengyuan

    2011-01-12

    The trigeminovascular nociception induced by electrical stimulation of the dura mater surrounding the superior sagittal sinus in anesthetized animals has been widely used as a model for investigation of the pathophysiology of vascular headache such as migraine. However, little is known whether pain behaviors can be induced using this model in conscious animals. Thus, to establish a new model of trigeminovascular nociception in conscious animals and to examine the effects of morphine and rizatriptan benzoate on nociceptive behaviors in this new model, we electrically stimulated the dura mater surrounding the superior sagittal sinus. We found that grooming and head-flick activities were altered partially in a frequency-dependent way and that frequencies ranging from 10 to 20 Hz more easily provoked these behaviors. Moreover, we also demonstrated that these behaviors were reduced by morphine and rizatriptan benzoate. Thus, this new model will provide a useful and appropriate tool to directly assess changes in the intensity of pain for further investigation of pathophysiological mechanisms of migraine in conscious animals.

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

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

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

  19. COMPARISON OF FATIGUE AND CREEP BEHAVIOR BETWEEN 2D AND 3D-C/SiC COMPOSITES

    Institute of Scientific and Technical Information of China (English)

    D. Han; S.R. Qiao; M. Li; J.T. Hou; X.J. Wu

    2004-01-01

    The differences of tension-tension fatigue and tensile creep characters of 2D-C/SiCand 3D-C/SiC composites have been scrutinized to meet the engineering needs. Experiments of tension-tension fatigue and tensile creep are carried out under vacuum high temperature condition. All of the high temperature fatigue curves are flat; the fatigue curves of the 2D-C/SiC are flatter and even parallel to the horizontal axis. While the tension-tension fatigue limit of the 3D-C/SiC is higher than that of the 2D-C/SiC, the fiber pullout length of the fatigue fracture surface of the 3D-C/SiC is longer than that of the 2D-C/SiC, and fracture morphology of the 3D-C/SiC is rougher, and pullout length of the fiber tows is longer. At the same time the 3D-C/SiC has higher tensile creep resistance. The tensile curve and the tensile creep curve of both materials consist of a series of flat step. These phenomena can be explained by the non-continuity of the damage.

  20. Experimental and Numerical Investigations of Fretting Fatigue Behavior for Steel Q235 Single-Lap Bolted Joints

    Directory of Open Access Journals (Sweden)

    Yazhou Xu

    2016-01-01

    Full Text Available This work aims to investigate the fretting fatigue life and failure mode of steel Q235B plates in single-lap bolted joints. Ten specimens were prepared and tested to fit the S-N curve. SEM (scanning electron microscope was then employed to observe fatigue crack surfaces and identify crack initiation, crack propagation, and transient fracture zones. Moreover, a FEM model was established to simulate the stress and displacement fields. The normal contact stress, tangential contact stress, and relative slipping displacement at the critical fretting zone were used to calculate FFD values and assess fretting fatigue crack initiation sites, which were in good agreement with SEM observations. Experimental results confirmed the fretting fatigue failure mode for these specimens. It was found that the crack initiation resulted from wear regions at the contact surfaces between plates, and fretting fatigue cracks occurred at a certain distance away from hole edges. The proposed FFD-N relationship is an alternative approach to evaluate fretting fatigue life of steel plates in bolted joints.

  1. Cognitive behavioral therapy for insomnia comorbid with COPD is feasible with preliminary evidence of positive sleep and fatigue effects

    Directory of Open Access Journals (Sweden)

    Kapella MC

    2011-11-01

    Full Text Available Mary C Kapella1, James J Herdegen2, Michael L Perlis3, Joan L Shaver4, Janet L Larson5, Julie A Law2, David W Carley11Center for Narcolepsy, Sleep and Health Research, Department of Biobehavioral Science, College of Nursing, 2Section of Pulmonary, Critical Care, Sleep and Allergy, College of Medicine, University of Illinois at Chicago, Chicago, IL, USA; 3Department of Psychiatry, University of Pennsylvania, Philadelphia, PA, USA; 4College of Nursing, University of Arizona, Tucson, AZ, USA; 5Division of Acute, Critical and Long Term Care Programs, University of Michigan School of Nursing, Ann Arbor, MI, USABackground: Many people with COPD report difficulties falling asleep or staying asleep, insufficient sleep duration, or nonrestorative sleep. Cognitive behavioral therapy for insomnia (CBT-I has proved effective not only in people with primary insomnia but also in people with insomnia comorbid with psychiatric and medical illness (eg, depression, cancer, and chronic pain. However, CBT-I has rarely been tested in those with COPD who have disease-related features that interfere with sleep and may lessen the effectiveness of such therapies. The purpose of this study was to determine the feasibility of applying a CBT-I intervention for people with COPD and to assess the impact of CBT-I on insomnia severity and sleep-related outcomes, fatigue, mood, and daytime functioning.Methods: The study had two phases. In Phase 1, a 6-weekly session CBT-I intervention protocol in participants with COPD was assessed to examine feasibility and acceptability. Phase 2 was a small trial utilizing a prospective two-group pre- and post-test design with random assignment to the six-session CBT-I or a six-session wellness education (WE program to determine the effects of each intervention, with both interventions being provided by a nurse behavioral sleep medicine specialist.Results: Fourteen participants (five in Phase 1 and nine in Phase 2 completed six sessions of

  2. Experimental Investigation of Fatigue Crack Growth Behavior in Friction Stir Welded 7075-T111 Aluminum Alloy Joints under Constant Stress Intensity Factor Range Control Testing (For L T Orientation Specimen)

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Yeui Han; Kim, Seon Jin [Pukyong Nat' l Univ., Busan (Korea, Republic of)

    2013-06-15

    In this study, as a series of studies aimed at investigating the spatial randomness of fatigue crack growth for friction stir welded (FSWed) 7075-T111 aluminum alloy joints, the fatigue crack growth behavior of FSWed 7075-T111 aluminum alloy joints was investigated for L T orientation specimens. Fatigue crack growth tests were conducted under constant stress intensity factor range (SEFOR) control for 5 specimens of the FSWed 7075-T111 aluminum alloy, including base metal (B M), heat affected zone (Haz), and weld metal (W M) specimens. The mean fatigue crack growth rate of W M specimens was found to be the highest, whereas that of Haz and W M specimens was the lowest. Furthermore, the variability of fatigue crack growth rate was found to be the highest in W M specimens and lowest in B M specimens.

  3. Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part I: Cyclic Deformation Behavior

    Science.gov (United States)

    Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

    2014-10-01

    In this study, the influence of cyclic strain amplitude on the evolution of cyclic stress-strain response and the associated cyclic deformation mechanisms in 316LN stainless steel with varying nitrogen content (0.07 to 0.22 wt pct) is reported in the temperature range 773 K to 873 K (500 °C to 600 °C). Two mechanisms, namely dynamic strain aging and secondary cyclic hardening, are found to strongly influence the cyclic stress response. Deformation substructures associated with both the mechanisms showed planar mode of deformation. These mechanisms are observed to be operative over certain combinations of temperature and strain amplitude. For strain amplitudes >0.6 pct, wavy or mixed mode of deformation is noticed to suppress both the mechanisms. Cyclic stress-strain curves revealed both single and dual-slope behavior depending on the test temperature. Increase in nitrogen content is found to increase the tendency toward planar mode of deformation, while increase in strain amplitude leads to transition from planar slip bands to dislocation cell/wall structure formation, irrespective of the nitrogen content in 316LN stainless steel.

  4. Fatigue limits of titanium-bar joints made with the laser and the electric resistance welding techniques: microstructural characterization and hardness properties.

    Science.gov (United States)

    Degidi, Marco; Nardi, Diego; Morri, Alessandro; Sighinolfi, Gianluca; Tebbel, Florian; Marchetti, Claudio

    2017-09-01

    Fatigue behavior of the titanium bars is of utmost importance for the safe and reliable operation of dental implants and prosthetic constructions based on these implants. To date, however, only few data are available on the fatigue strength of dental prostheses made with electric resistance welding and laser welding techniques. This in-vitro study highlighted that although the joints made with the laser welding approach are credited of a superior tensile strength, joints made with electric resistance welding exhibited double the minimum fatigue strength with respect to the joints made with laser welding (120 vs 60 N).

  5. Effect of composition and processing on the thermal fatigue and toughness of high performance die steels. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Wallace, J.F.; Wang, Y.; Schwam, D.

    1997-06-01

    The objective of this study was to improve average die life by optimizing die steel composition and the die processing. Four different steels, K,Q,C and Premium Grade H-13 have been investigated for thermal fatigue resistance and toughness. Optimum heat treatment processing has been determined for each steel with respect to austenitizing temperature and tempering conditions. The effect of the quenching rate on the thermal fatigue resistance and toughness of the die steels and the effect of Electro-Discharge Machining (EDM) on the thermal fatigue resistance were also determined. The immersion thermal fatigue specimen developed at CWRU was used to determine the thermal fatigue resistance as characterized by the two parameters of average maximum crack length and total crack area. The Charpy V-notch impact test was used over a -100{degrees}F to 450{degrees}F testing temperature range to evaluate the toughness and the brittle-ductile transition behavior. K steel has been identified as superior in performance compared to Premium Grade H-13. Q and C provide lower toughness and thermal fatigue resistance than H-13. Faster cooling rates provide higher thermal fatigue resistance and toughness. Higher austenitizing temperatures such as 1925{degrees}F compared to 1875{degrees}F provide better thermal fatigue resistance, but lower austenitizing temperatures of 1875{degrees}F provide better toughness. Higher hardness improves thermal fatigue resistance, but reduces toughness. A minimum of Rc 46 hardness is desired for aluminum die casting dies. EDM reduces the thermal fatigue resistance compared to conventional machining operations. When the EDM process of multiple small steps of decreasing energy and post-EDM treatments are employed, the effect can be reduced to a very slight amount. Preliminary evidence of the superior performance of the K steel has been provided by ongoing field testing of inserts in multiple cavity dies.

  6. 粉末高温合金FGH97疲劳裂纹扩展行为%Fatigue behavior of powder metallurgy superalloy FGH97

    Institute of Scientific and Technical Information of China (English)

    佴启亮; 董建新; 张麦仓; 郑磊; 姚志浩

    2016-01-01

    测定不同晶粒尺寸、γ'相以及不同Hf含量的粉末高温合金FGH97在650℃高温条件下的疲劳裂纹扩展速率,并将其与FGH95和FGH96两代粉末合金的疲劳裂纹扩展速率进行对比. 用定量分析的方法对FGH97合金在疲劳断裂各个阶段的行为特征进行分析. 较大晶粒尺寸的FGH97合金具有较低的裂纹扩展速率,合理的二次和三次γ'相匹配析出,可以获得较高的疲劳寿命;Hf元素的添加使合金的整体疲劳寿命增大;FGH97合金与FGH95和FGH96相比,具有较高的疲劳裂纹萌生抗力,更低的高温疲劳裂纹扩展速率.%The fatigue crack growth rates of powder metallurgy ( P/M) superalloy FGH97 with different grain sizes,γ'phase sizes and Hf contents were measured at a 650℃ high temperature condition and compared with those of FGH95 and FGH96 alloys. The fatigue fracture behavior characteristic of FGH97 alloy in each stage was analyzed by the quantitative analysis method. It is found that FGH97 alloy with coarser grains has a lower fatigue crack growth rate. Reasonable match of secondary and tertiary γ' phases and Hf addition can get a higher fatigue life. Compared with FGH95 and FGH96 alloys, FGH97 alloy has the highest fatigue cack intiation resistance and exihibits the lowest fatigue crack propagation rate at high temperature.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-10-06

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

  8. Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C

    Science.gov (United States)

    Castelli, Michael G.

    1994-01-01

    The isothermal fatigue damage and life behaviors of SCS-6/Timetal 21S (0/90)s were investigated at 650 C. Strain ratcheting and degradation of the composite's static elastic modulus were carefully monitored as functions of cycles to indicate damage progression. Extensive fractographic and metallographic analyses were conducted to determine damage/failure mechanisms. Resulting fatigue lives show considerable reductions in comparison to (0) reinforced titanium matrix composites subjected to comparable conditions. Notable stiffness degradations were found to occur after the first cycle of loading, even at relatively low maximum stress levels, where cyclic lives are greater than 25,000 cycles. This was attributed to the extremely weak fiber/matrix bond which fails under relatively low transverse loads. Stiffness degradations incurred on first cycle loadings and degradations thereafter were found to increase with increasing maximum stress. Environmental effects associated with oxidation of the (90) fiber interfaces clearly played a role in the damage mechanisms as fracture surfaces revealed environment assisted matrix cracking along the (90) fibers. Metallographic analysis indicated that all observable matrix fatigue cracks initiated at the (90) fiber/matrix interfaces. Global de-bonding in the loading direction was found along the (90) fibers. No surface initiated cracks were evident and minimal if any (0) fiber cracking was visible.

  9. Aging behavior and fatigue crack propagation of high Zn-containing Al-Zn-Mg-Cu alloys with zinc variation

    Directory of Open Access Journals (Sweden)

    Kai Wen

    2017-04-01

    Full Text Available In the present work, the influence of two-step aging treatments on hardness, electrical conductivity and mechanical properties of two high Zn-containing Al-Zn-Mg-Cu alloys with zinc content variation was investigated and the detailed T76 aging parameters were proposed. The microstructure of the precipitates were studied by transmission electron microscopy (TEM and high-resolution transmission electron microscopy (HREM and then quantitatively investigated with the aid of an image analysis. The fatigue performances were researched by the fatigue crack propagation (FCP rate test and fracture morphology was observed with scanning electron microscopy (SEM. The results show that the matrix precipitate size distributions of both alloys had significant difference, so as to fatigue crack propagation rates and fracture appearance. The shear and bypass mechanisms of dislocation-precipitate interactions were employed to explain the difference. Among the shearable precipitates, the proportion of larger size precipitates for the higher zinc content alloy is bigger than that for the lower zinc content alloy. The coarse shearable precipitates hinder the propagation of the fatigue cracks, leading to inferior FCP rate. For both alloys, the shear mechanism possesses the dominant factor, finally causing a preponderance in the FCP resistance for the higher zinc content alloy than the lower one.

  10. Ductile Damage and Fatigue Behavior of Semi-Finished Tailored Blanks for Sheet-Bulk Metal Forming Processes

    Science.gov (United States)

    Besserer, Hans-Bernward; Hildenbrand, Philipp; Gerstein, Gregory; Rodman, Dmytro; Nürnberger, Florian; Merklein, Marion; Maier, Hans Jürgen

    2016-03-01

    To produce parts from sheet metal with thickened functional elements, bulk forming operations can be employed. For this new process class, the term sheet-bulk metal forming has been established recently. Since sheet-bulk metal forming processes such as orbital forming generates triaxial stress and strain states, ductile damage is induced in the form of voids in the microstructure. Typical parts will experience cyclic loads during service, and thus, the influence of ductile damage on the fatigue life of parts manufactured by orbital forming is of interest. Both the formation and growth of voids were characterized following this forming process and then compared to the as-received condition of the ferritic deep drawing steel DC04 chosen for this study. Subsequent to the forming operation, the specimens were fatigued and the evolution of ductile damage and the rearrangement of the dislocation networks occurring during cyclic loading were determined. It was shown, that despite an increased ductile damage due to the forming process, the induced strain hardening has a positive effect on the fatigue life of the material. However, by analyzing the fatigued specimens a development of the ductile damage by an increasing number of voids and a change in the void shape were detected.

  11. Effect of aging time and aging temperature on fatigue and fracture behavior of 6063 aluminum alloy under seawater influence

    Energy Technology Data Exchange (ETDEWEB)

    Siddiqui, R.A. [Department of Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khod 123 (Oman); Abdul-Wahab, S.A. [Department of Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khod 123 (Oman)], E-mail: sabah1@squ.edu.om; Pervez, T. [Department of Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khod 123 (Oman)

    2008-07-01

    This paper describes experimentally the effect of seawater corrosion, aging time, and aging temperature on the fatigue resistance property of 6063 aluminum alloy. The 6063 aluminum alloy that was used for the study was heat treated and soaked in seawater for different intervals of time between 2 and 30 weeks. It was found that the maximum fatigue resistance property in the 6063 aluminum alloy was observed when aged between 7 and 9 h and heat treated at temperatures between 160 {sup o}C and 200 {sup o}C. Generally at constant load, the results indicated that the number of cycles to fail the 6063 aluminum alloy decreased with increasing the soaking time in seawater. Moreover, fracture surfaces were considered and studied under a scanning electron microscope (SEM). The results showed that the brittle fracture pattern tended to occur with the increase in aging time and temperature. The fatigue striations were observed very clearly at low and peak aging temperature. The increase in the fatigue resistance property with aging time was linked with the vacancies assisted diffusion mechanism and also by the hindering of dislocation movement by impure atoms.

  12. Crack Initiation and Growth Behavior at Corrosion Pit in 7075-T6 Under Biaxial and Uniaxial Fatigue

    Science.gov (United States)

    2014-06-19

    general conical , hemispherical, and roughly saucer-shaped for steel and many alloys [41], as shown in Figure 2.2. Pits usually nucleate at chemical or...performed in a piezoelectric resonance system. Their results indicated that the presence of corrosion pits notably reduces the fatigue life of the

  13. What Happened to the "Superior Abilities" in Adults with Dyslexia and High IQs? A Behavioral and Neurological Illustration

    Science.gov (United States)

    Gilger, Jeffrey W.; Olulade, Olumide A.

    2013-01-01

    Observable behavior, such as test scores, is the gold standard by which we make judgments about levels of function, grade placements, and the presence/absence of pathology. Individual differences in test performance have long intrigued researchers and clinicians, and some have noted how people can come up with essentially the same answers using…

  14. "My in-group is superior!": susceptibility for radical right-wing attitudes and behaviors in Dutch youth

    NARCIS (Netherlands)

    Doosje, B.; van den Bos, K.; Loseman, A.; Feddes, A.R.; Mann, L.

    2012-01-01

    In this study among Dutch youth (N = 1086), we focus on the determinants of the susceptibility for adopting radical right-wing attitudes and behaviors. By means of structural equation modeling, we find that (a) perceived injustice, (b) perceived group threat, (c) relative deprivation, and (d)

  15. What Happened to the "Superior Abilities" in Adults with Dyslexia and High IQs? A Behavioral and Neurological Illustration

    Science.gov (United States)

    Gilger, Jeffrey W.; Olulade, Olumide A.

    2013-01-01

    Observable behavior, such as test scores, is the gold standard by which we make judgments about levels of function, grade placements, and the presence/absence of pathology. Individual differences in test performance have long intrigued researchers and clinicians, and some have noted how people can come up with essentially the same answers using…

  16. Effects of large amounts of hydrogen on the fatigue crack growth behavior of torsional prestrained carbon steel

    Directory of Open Access Journals (Sweden)

    Yuta Matsuda

    2016-01-01

    Full Text Available The effects of large amounts of hydrogen on the fatigue crack growth properties of torsional prestrained ferritic–pearlitic low-carbon steel were investigated. Hydrogen-precharged specimens were produced by conducting cathodic charge to the virgin material and to torsional prestrained JIS-S10C and JISS25C steels (hereafter S10C and S25C steels. Rotating bending fatigue tests were conducted in air at room temperature. Hydrogen content, CH, increased with torsional prestrain for both S10C and S25C steels; the CH of the torsional prestrained S25C steel precharged with hydrogen was lower than that of S10C at the same torsional prestrain. No clear difference between the maximum CH values of the torsional fractured S10C and S25C hydrogen-precharged steel specimens. With respect to crack initiation, there was no obvious difference between the uncharged and precharged specimens in spite of the large amount of CH induced by torsional prestrain. The acceleration of fatigue crack growth by hydrogen was the main cause of the decreased fatigue life. For the virgin material, hydrogen had no obvious effect on the fatigue crack growth rate. In contrast, for the torsional prestrained materials, the acceleration ratios, {(da/dNH/(da/dNU}, increased with the torsional prestrain and CH. However, {(da/dNH/(da/dNU} did not exceed the value of about 30, even when a large amount of hydrogen was charged (10.0 ≤ CH ≤ 30.3 mass ppm. A hydrogen content threshold was found; hydrogen content above this limit enhances the growth of the non-propagated crack, even for metals with lower hardness (HV < 200.

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

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2012-04-01

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

  18. Experimental Study on Shear Fatigue Behavior and Stiffness Performance of Warm Mix Asphalt by adding Synthetic Wax

    CERN Document Server

    Petit, Christophe; Canestrari, Francesco; Pannunzio, Valter; Virgili, Amadeo

    2012-01-01

    Synthetic waxes produced by standard and registered processes may be used to manufacture Warm Mix Asphalt (WMA), which is a modified asphalt concrete produced, applied and compacted at temperatures below those typically required. This feature leads to environmental benefits, such as reduced energy consumption, gas and fume emissions, as well as to economic/operational advantages, such as lower production costs and greater hauling distances for extended construction seasons with tighter schedules. The present article serves to compare the mechanical performance of a WMA produced by adding synthetic wax with a traditional Hot Mix Asphalt (HMA) specimen, in terms of shear fatigue response and both complex and stiffness moduli. The experimental results and related modeling work demonstrate that adding synthetic wax into the WMA composition does not hinder either the destructive or non-destructive performance of an HMA, and this finding is corroborated by respectively measuring fatigue life and stiffness.

  19. Simulation Methods for High-Cycle Fatigue-Driven Delamination using Cohesive Zone Models - Fundamental Behavior and Benchmark Studies

    DEFF Research Database (Denmark)

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

    2015-01-01

    A novel computational method for simulating fatigue-driven delamination cracks in composite laminated structures under cyclic loading based on a cohesive zone model [2] and new benchmark studies with four other comparable methods [3-6] are presented. The benchmark studies describe and compare...... the traction-separation response in the cohesive zone and the transition phase from quasistatic to fatigue loading for each method. Furthermore, the accuracy of the predicted crack growth rate is studied and compared for each method. It is shown that the method described in [2] is significantly more accurate...... than the other methods [3-6]. Finally, studies are presented of the dependency and sensitivity to the change in different quasi-static material parameters and model specific fitting parameters. It is shown that all the methods except [2] rely on different parameters which are not possible to determine...

  20. Creep-Rupture and Fatigue Behavior of a Notched Oxide/Oxide Ceramic Matrix Composite at Elevated Temperature

    Science.gov (United States)

    2008-06-01

    ultrasonic bath of deionized water to remove any excess debris and then dried in an oven at 90°C for 30 minutes. 16 Figure 9. Specimen dimensions...Figure 107. 155 MPa Fatigue (right) 100 Bibliography 1. “3M Ceramic Fiber Typical Properties,” Nextel™ Ceramic Textiles Technical Notebook... ultrasonic C-scans,” Composites Science and Technology, 61[11], 1561-1570 (2001). 20. Kramb, Victoria A., Reji John and Larry P. Zawada. “Notched

  1. Corrosion Fatigue Crack Growth Behavior at Notched Hole in 7075 T6 Under Different Biaxial Stress Ratios

    Science.gov (United States)

    2016-08-18

    strain energy release rate I mode one (opening) K stress intensity factor (MPa*m^0.5) M molar mass R stress ratio for cyclic loading (unit less) r...Finally, 7 the third phase of the fatigue failure occurs when the resistance is exceeded, and a structure occurs, Figure 2.1 [30]. Figure 2.1...Alloy 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF PAGES 92 19a. NAME OF RESPONSIBLE PERSON Shankar

  2. Static and dynamic fatigue behavior of topology designed and conventional 3D printed bioresorbable PCL cervical interbody fusion devices.

    Science.gov (United States)

    Knutsen, Ashleen R; Borkowski, Sean L; Ebramzadeh, Edward; Flanagan, Colleen L; Hollister, Scott J; Sangiorgio, Sophia N

    2015-09-01

    Recently, as an alternative to metal spinal fusion cages, 3D printed bioresorbable materials have been explored; however, the static and fatigue properties of these novel cages are not well known. Unfortunately, current ASTM testing standards used to determine these properties were designed prior to the advent of bioresorbable materials for cages. Therefore, the applicability of these standards for bioresorbable materials is unknown. In this study, an image-based topology and a conventional 3D printed bioresorbable poly(ε)-caprolactone (PCL) cervical cage design were tested in compression, compression-shear, and torsion, to establish their static and fatigue properties. Difficulties were in fact identified in establishing failure criteria and in particular determining compressive failure load. Given these limitations, under static loads, both designs withstood loads of over 650 N in compression, 395 N in compression-shear, and 0.25 Nm in torsion, prior to yielding. Under dynamic testing, both designs withstood 5 million (5M) cycles of compression at 125% of their respective yield forces. Geometry significantly affected both the static and fatigue properties of the cages. The measured compressive yield loads fall within the reported physiological ranges; consequently, these PCL bioresorbable cages would likely require supplemental fixation. Most importantly, supplemental testing methods may be necessary beyond the current ASTM standards, to provide more accurate and reliable results, ultimately improving preclinical evaluation of these devices. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. Time-Dependent Fatigue Crack Propagation Behavior of Two Solid-Solution-Strengthened Ni-Based Superalloys—INCONEL 617 and HAYNES 230

    Science.gov (United States)

    Ma, Longzhou; Roy, Shawoon K.; Hasan, Muhammad H.; Pal, Joydeep; Chatterjee, Sudin

    2012-02-01

    The fatigue crack propagation (FCP) as well as the sustained loading crack growth (SLCG) behavior of two solid-solution-strengthened Ni-based superalloys, INCONEL 617 (Special Metals Corporation Family of Companies) and HAYNES 230 (Haynes International, Inc., Kokomo, IN), were studied at increased temperatures in laboratory air under a constant stress-intensity-factor ( K) condition. The crack propagation tests were conducted using a baseline cyclic triangular waveform with a frequency of 1/3 Hz. Various hold times were imposed at the maximum load of a fatigue cycle to study the hold time effect. The results show that a linear elastic fracture mechanics (LEFM) parameter, stress intensity factor ( K), is sufficient to describe the FCP and SLCG behavior at the testing temperatures ranging from 873 K to 1073 K (600 °C to 800 °C). As observed in the precipitation-strengthened superalloys, both INCONEL 617 and HAYNES 230 exhibited the time-dependent FCP, steady SLCG behavior, and existence of a damage zone ahead of crack tip. A thermodynamic equation was adapted to correlate the SLCG rates to determine thermal activation energy. The fracture modes associated with crack propagation behavior were discussed, and the mechanism of time-dependent FCP as well as SLCG was identified. Compared with INCONEL 617, the lower crack propagation rates of HAYNES 230 under the time-dependent condition were ascribed to the different fracture mode and the presence of numerous W-rich M6C-type and Cr-rich M23C6-type carbides. Toward the end, a phenomenological model was employed to correlate the FCP rates at cycle/time-dependent FCP domain. All the results suggest that an environmental factor, the stress assisted grain boundary oxygen embrittlement (SAGBOE) mechanism, is mainly responsible for the accelerated time-dependent FCP rates of INCONEL 617 and HAYNES 230.

  4. Fatigue (PDQ)

    Science.gov (United States)

    ... of daily living . Better quality of life . More satisfaction with life. A greater sense of well-being. ... and decrease fatigue. The importance of eating enough food and drinking enough fluids. Physical therapy for patients ...

  5. Carbon nanotube reinforced hybrid composites: Computational modeling of environmental fatigue and usability for wind blades

    DEFF Research Database (Denmark)

    Dai, Gaoming; Mishnaevsky, Leon

    2015-01-01

    The potential of advanced carbon/glass hybrid reinforced composites with secondary carbon nanotube reinforcement for wind energy applications is investigated here with the use of computational experiments. Fatigue behavior of hybrid as well as glass and carbon fiber reinforced composites...... with the secondary CNT reinforcements (especially, aligned tubes) present superior fatigue performances than those without reinforcements, also under combined environmental and cyclic mechanical loading. This effect is stronger for carbon composites, than for hybrid and glass composites....... automatically using the Python based code. 3D computational studies of environment and fatigue analyses of multiscale composites with secondary nano-scale reinforcement in different material phases and different CNTs arrangements are carried out systematically in this paper. It was demonstrated that composites...

  6. Analysis of the nonlinear dynamic behavior of power systems using normal forms of superior order; Analisis del comportamiento dinamico no lineal de sistemas de potencia usando formas normales de orden superior

    Energy Technology Data Exchange (ETDEWEB)

    Marinez Carrillo, Irma

    2003-08-01

    This thesis investigates the application of parameter disturbance methods of analysis to the nonlinear dynamic systems theory, for the study of the stability of small signal of electric power systems. The work is centered in the determination of two fundamental aspects of interest in the study of the nonlinear dynamic behavior of the system: the characterization and quantification of the nonlinear interaction degree between the fundamental ways of oscillation of the system and the study of the ways with greater influence in the response of the system in the presence of small disturbances. With these objectives, a general mathematical model, based on the application of the expansion in series of power of the nonlinear model of the power system and the theory of normal forms of vector fields is proposed for the study of the dynamic behavior of the power system. The proposed tool generalizes the existing methods in the literature to consider effects of superior order in the dynamic model of the power system. Starting off of this representation, a methodology is proposed to obtain analytical solutions of loop back and the extension of the existing methods is investigated to identify and quantify the of interaction degree among the fundamental ways of oscillation of the system. The developed tool allows, from analytical expressions of loop backs, the development of analytical measures to evaluate the stress degree in the system, the interaction between the fundamental ways of oscillation and the determination of stability borders. The conceptual development of the proposed method in this thesis offers, on the other hand, a great flexibility to incorporate detailed models of the power system and the evaluation of diverse measures of the nonlinear modal interaction. Finally, the results are presented of the application of the method of analysis proposed for the study of the nonlinear dynamic behavior in a machine-infinite bus system considering different modeled degrees

  7. [Auditory fatigue].

    Science.gov (United States)

    Sanjuán Juaristi, Julio; Sanjuán Martínez-Conde, Mar

    2015-01-01

    Given the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor. Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. We used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. Using a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15minutes; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation. No fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials. Copyright © 2013 Elsevier España, S.L.U. y Sociedad Española de Otorrinolaringología y Patología Cérvico-Facial. All rights reserved.

  8. Effects of Plasma ZrN Metallurgy and Shot Peening Duplex Treatment on Fretting Wear and Fretting Fatigue Behavior of Ti6Al4V Alloy

    Directory of Open Access Journals (Sweden)

    Jingang Tang

    2016-03-01

    Full Text Available A metallurgical zirconium nitride (ZrN layer was fabricated using glow metallurgy using nitriding with zirconiuming prior treatment of the Ti6Al4V alloy. The microstructure, composition and microhardness of the corresponding layer were studied. The influence of this treatment on fretting wear (FW and fretting fatigue (FF behavior of the Ti6Al4V alloy was studied. The composite layer consisted of an 8-μm-thick ZrN compound layer and a 50-μm-thick nitrogen-rich Zr–Ti solid solution layer. The surface microhardness of the composite layer is 1775 HK0.1. A gradient in cross-sectional microhardness distribution exists in the layer. The plasma ZrN metallurgical layer improves the FW resistance of the Ti6Al4V alloy, but reduces the base FF resistance. This occurs because the improvement in surface hardness results in lowering of the toughness and increasing in the notch sensitivity. Compared with shot peening treatment, plasma ZrN metallurgy and shot peening composite treatment improves the FW resistance and enhances the FF resistance of the Ti6Al4V alloy. This is attributed to the introduction of a compressive stress field. The combination of toughness, strength, FW resistance and fatigue resistance enhance the FF resistance for titanium alloy.

  9. Effect of oxidation on the fatigue crack propagation behavior of Z3CN20.09M dyplex stainless steel in high temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Huan Chun; Yang, Bin [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing (China); Chen, Yue Feng; Chen, Xu Dong [Collaborative Innovation Center of Steel Technology, Beijing (China)

    2017-06-15

    The fatigue crack propagation behaviors of Z3CN20.09M duplex stainless steel (DSS) were investigated by studying oxide films of specimens tested in 290°C water and air. The results indicate that a full oxide film that consisted of oxides and hydroxides was formed in 290°C water. By contrast, only a half-baked oxide film consisting of oxides was formed in 290°C air. Both environments are able to deteriorate the elastic modulus and hardness of the oxide films, especially the 290°C water. The fatigue lives of the specimens tested in 290°C air were about twice of those tested in 290°C water at all strain amplitudes. Moreover, the crack propagation rates of the specimen tested in 290°C water were confirmed to be faster than those tested in 290°C air, which was thought to be due to the deteriorative strength of the oxide films induced by the mutual promotion of oxidation and crack propagation at the crack tip. It is noteworthy that the crack propagation can be postponed by the ferrite phase in the DSS, especially when the specimens were tested in 290°C water.

  10. In vitro mechanical fatigue behavior of poly-ɛ-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel.

    Science.gov (United States)

    Panadero, J A; Vikingsson, L; Gomez Ribelles, J L; Lanceros-Mendez, S; Sencadas, V

    2015-07-01

    Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long-term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behavior of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow's criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles.

  11. Investigation of structure-property relationships of polyisobutylene-based biomaterials: Morphology, thermal, quasi-static tensile and long-term dynamic fatigue behavior.

    Science.gov (United States)

    Götz, C; Lim, G T; Puskas, J E; Altstädt, V

    2012-06-01

    This study examines the morphology, thermal, quasi-static and long-term dynamic creep properties of one linear and three arborescent polyisobutylene-based block copolymers (L_SIBS31, D_IBS16, D_IBS27 and D_IBS33). Silicone rubber, a common biopolymer, was considered as a benchmark material for comparison. A unique hysteretic testing methodology of Stepwise Increasing Load Test (SILT) and Single Load Test (SLT) was used in this study to evaluate the long-term dynamic fatigue performance of these materials. Our experimental findings revealed that the molecular weight of polyisobutylene (PIB) and polystyrene (PS) arms [M(n)(PIB(arm)) and M(n)(PS(arm))], respectively had a profound influence on the nano-scaled phase separation, quasi-static tensile, thermal transition, and dynamic creep resistance behaviors of these PIB-based block copolymers. However, silicone rubber outperformed the PIB-based block copolymers in terms of dynamic creep properties due to its chemically crosslinked structure. This indicates a need for a material strategy to improve the dynamic fatigue and creep of this class of biopolymers to be considered as alternative to silicone rubber for biomedical devices.

  12. Effects of Plasma ZrN Metallurgy and Shot Peening Duplex Treatment on Fretting Wear and Fretting Fatigue Behavior of Ti6Al4V Alloy.

    Science.gov (United States)

    Tang, Jingang; Liu, Daoxin; Zhang, Xiaohua; Du, Dongxing; Yu, Shouming

    2016-03-23

    A metallurgical zirconium nitride (ZrN) layer was fabricated using glow metallurgy using nitriding with zirconiuming prior treatment of the Ti6Al4V alloy. The microstructure, composition and microhardness of the corresponding layer were studied. The influence of this treatment on fretting wear (FW) and fretting fatigue (FF) behavior of the Ti6Al4V alloy was studied. The composite layer consisted of an 8-μm-thick ZrN compound layer and a 50-μm-thick nitrogen-rich Zr-Ti solid solution layer. The surface microhardness of the composite layer is 1775 HK0.1. A gradient in cross-sectional microhardness distribution exists in the layer. The plasma ZrN metallurgical layer improves the FW resistance of the Ti6Al4V alloy, but reduces the base FF resistance. This occurs because the improvement in surface hardness results in lowering of the toughness and increasing in the notch sensitivity. Compared with shot peening treatment, plasma ZrN metallurgy and shot peening composite treatment improves the FW resistance and enhances the FF resistance of the Ti6Al4V alloy. This is attributed to the introduction of a compressive stress field. The combination of toughness, strength, FW resistance and fatigue resistance enhance the FF resistance for titanium alloy.

  13. Effect of Microstructures on Fatigue Crack Growth Behavior of Friction Stir Processed NiAl Bronze Alloy

    Science.gov (United States)

    Lv, Yuting; Ding, Yang; Han, Yuanfei; Wu, Laizhi; Wang, Liqiang; Lu, Weijie

    2017-01-01

    Abstract: Friction stir processed (FSPed) NAB alloy exhibits inhomogeneous microstructures that can be divided into three subregions from the top surface to the bottom according to α phase morphologies: Widmanstatten α subregion, banded α colonies, and stream-like α colonies. In this study, a constant stress intensity range (ΔK) was used for each sample to study the effect of microstructures on the fatigue crack growth rate (FCGR) of FSPed NAB alloy. The results show that α phase in banded and stream-like α colonies experiences completely dynamic recrystallization and forms equiaxed α grains during FSP. The FCGR of FSPed NAB alloy continuously decreases from the top surface to the bottom. In the subregion with stream-like α colonies, the alloy containing a higher content of equiaxed α grains and fine κ iv phase, and less retained β (β') phase exhibits the best FCG resistance. The equiaxed α grains deflect the main crack and increase crack tortuosity effect, which make a main contribution to FCG resistance of FSPed NAB alloy, while martensite β' phase produced during FSP accelerates its fatigue crack growth. Compared to matrix alloy, FSPed NAB alloy exhibits better FCG resistance only at high ΔK levels. At low ΔK levels, the crack deflection effect caused by coarser κ phase in the matrix alloy obviously improves its FCG resistance. With the increasing ΔK, the aforementioned crack deflection effect gradually diminishes and fatigue crack prefers to propagate in a flat way, resulting in higher FCGR of matrix alloy.

  14. Chronic Fatigue Syndrome

    Science.gov (United States)

    Chronic fatigue syndrome (CFS) is a disorder that causes extreme fatigue. This fatigue is not the kind of tired feeling that ... activities. The main symptom of CFS is severe fatigue that lasts for 6 months or more. You ...

  15. Human middle longitudinal fascicle: Segregation and behavioral-clinical implications of two distinct fiber connections linking temporal pole and superior temporal gyrus with the angular gyrus or superior parietal lobule using multi-tensor tractography

    Science.gov (United States)

    Makris, N.; Preti, M.G.; Wassermann, D.; Rathi, Y.; Papadimitriou, G. M.; Yergatian, C.; Dickerson, B. C.; Shenton, M. E.; Kubicki, M.

    2013-01-01

    The middle longitudinal fascicle (MdLF) is a major fiber connection running principally between the superior temporal gyrus and the parietal lobe, neocortical regions of great biological and clinical interest. Although one of the most prominent cerebral association fiber tracts it has only recently been discovered in humans. In this high angular resolution diffusion imaging (HARDI) MRI study, we delineated the two major fiber connections of the human MdLF, by examining morphology, topography, cortical connections, biophysical measures, volume and length in seventy-four brains. These two fiber connections course together through the dorsal temporal pole and the superior temporal gyrus maintaining a characteristic topographic relationship in the mediolateral and ventrodorsal dimensions. As these pathways course towards the parietal lobe, they split to form separate fiber pathways, one following a ventrolateral trajectory and connecting with the angular gyrus and the other following a dorsomedial route and connecting with the superior parietal lobule. Based on the functions of their cortical affiliations, we suggest that the superior temporal-angular connection of the MdLF, i.e., STG(MdLF)AG plays a role in language and attention, whereas the superior temporal-superior parietal connection of the MdLF, i.e., STG(MdLF)SPL is involved in visuospatial and integrative audiovisual functions. Furthermore, the MdLF may have clinical implications in neurodegenerative disorders such as primary progressive aphasia, frontotemporal dementia, posterior cortical atrophy, corticobulbar degeneration and Alzheimer’s disease as well as attention-deficit/hyperactivity disorder and schizophrenia. PMID:23686576

  16. Creep, Fatigue and Fracture Behavior of Environmental Barrier Coating and SiC-SiC Ceramic Matrix Composite Systems: The Role of Environment Effects

    Science.gov (United States)

    Zhu, Dongming; Ghosn, Louis J.

    2015-01-01

    Advanced environmental barrier coating (EBC) systems for low emission SiCSiC CMC combustors and turbine airfoils have been developed to meet next generation engine emission and performance goals. This presentation will highlight the developments of NASAs current EBC system technologies for SiC-SiC ceramic matrix composite combustors and turbine airfoils, their performance evaluation and modeling progress towards improving the engine SiCSiC component temperature capability and long-term durability. Our emphasis has also been placed on the fundamental aspects of the EBC-CMC creep and fatigue behaviors, and their interactions with turbine engine oxidizing and moisture environments. The EBC-CMC environmental degradation and failure modes, under various simulated engine testing environments, in particular involving high heat flux, high pressure, high velocity combustion conditions, will be discussed aiming at quantifying the protective coating functions, performance and durability, and in conjunction with damage mechanics and fracture mechanics approaches.

  17. Recovery from Fatigue

    Science.gov (United States)

    1973-06-30

    napping behavior between nappers and non- nappers is discussed. Descriptors: Fatigue, Napping, Performance, Sleep , Psycho- physiology, Electrodermal ...capability. The present study seeks to address the physiological differences between the kind of sleep activity in which nappers engage, as opposed to...being awakened shortly after the beginning of a nap results in an unusual pattern of sleep activity probably associated with more active monitoring of

  18. Cumulative fatigue damage models

    Science.gov (United States)

    Mcgaw, Michael A.

    1988-01-01

    The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.

  19. Seafarer fatigue

    DEFF Research Database (Denmark)

    Jepsen, Jørgen Riis; Zhao, Zhiwei; van Leeuwen, Wessel M. A.

    2015-01-01

    Background: The consequences of fatigue for the health and safety of seafarers has caused concern in the industry and among academics, and indicates the importance of further research into risk factors and preventive interventions at sea. This review gives an overview of the key issues relating...

  20. Study on thermal fatigue behavior of 8407 steel with surface aluminization and oxidation treatment%渗铝氧化8407钢表面热疲劳行为研究

    Institute of Scientific and Technical Information of China (English)

    孙健

    2012-01-01

    Thermal fatigue test was performed with cycle heating method to compare thermal fatigue behaviors of 8407 steel samples with and without aluminization and oxidation treatment. In the test, thermal fatigue crack morphology formed on the surface was observed by SEM after 400 cycles, and then variations of initiating rate and propagating rate of thermal fatigue main crack with cycles were investigated. Moreover, the thermal fatigue property was judged according to the length of the thermal fatigue main crack. The results show that the surface aluminization and oxidation treatment can improve both the initiating resistance and propagating resistance of thermal fatigue crack.%采用循环加热法进行热疲劳实验,对比研究了表面未处理和表面渗铝氧化处理8407钢样的热疲劳行为.实验中,利用扫描电镜观察循环400周次后试样表面产生的热疲劳裂纹形貌,考察了热疲劳主裂纹的萌生与扩展速度随循环周次的变化.此外,根据主裂纹长度L的大小评判了热疲劳性能.研究结果表明,表面渗铝氧化处理能够同时提高热疲劳裂纹萌生抗力和扩展抗力.

  1. 钢质蜂窝夹芯梁高温疲劳试验及寿命预测研究%Investigation on the fatigue behaviors and life prediction of steel honeycomb sandwich beams

    Institute of Scientific and Technical Information of China (English)

    芦颉; 邹广平; 曹扬; 唱忠良; 刘宝君

    2011-01-01

    针对实际工程中钢质蜂窝夹芯结构在热环境下的疲劳耐久性及寿命问题,开展了400℃下的三点弯曲疲劳试验研究,得到S-N曲线.基于刚度退化,提出一种用于该类材料在高温下的疲劳寿命预测模型和损伤演化模型.该方法允许预测不同载荷水平下的疲劳寿命,避免了大量重复性疲劳试验.应用于模型的参数与材料性质、高温等试验条件有关.借助简单模型,完成了钢质蜂窝梁高温寿命预测及损伤演化预测,预测值与试验值吻合较好.%In the industrial field, an investigation on how temperature can affect damage and fatigue life of a honeycomb sandwich structure is significant. The aim of this work is to investigate fatigue behaviors of the steel honeycomb sandwich beams at 400℃ by three-point bending fatigue experiments. An S-N curve was obtained. Based on stiffness degradation, life prediction and damage evolution models were developed. This approach allowed the prediction of fatigue life under different load levels while avoiding a large number of repetitive fatigue tests. Parameters used in the model depended on the material properties and high temperature test conditions among other things. The developed models were applied to analyze the fatigue life and damage evolution of steel honeycomb sandwich specimens under fatigue. The results show that experimental and prediction results were in good agreement. Thus the proposed method is feasible.

  2. Fatigue damage mechanisms in polymer matrix composites

    OpenAIRE

    1997-01-01

    Polymer matrix composites are finding increased use in structural applications, in particular for aerospace and automotive purposes. Mechanical fatigue is the most common type of failure of structures in service. The relative importance of fatigue has yet to be reflected in design where static conditions still prevail. The fatigue behavior of composite materials is conventionally characterized by a Wöhler or S-N curve. For every new material with a new lay-up, altered constituents or differen...

  3. Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory

    Science.gov (United States)

    Li, Mengjiao; Wang, Junyong; Zhang, Peng; Deng, Qinglin; Zhang, Jinzhong; Jiang, Kai; Hu, Zhigao; Chu, Junhao

    2017-02-01

    The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567).

  4. Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory

    Science.gov (United States)

    Li, Mengjiao; Wang, Junyong; Zhang, Peng; Deng, Qinglin; Zhang, Jinzhong; Jiang, Kai; Hu, Zhigao; Chu, Junhao

    2017-01-01

    The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567). PMID:28211893

  5. Effects of flexural fatigue loading on thermal expansion behavior of 2D-C/C composites%弯-弯疲劳加载对2D-C/C复合材料热膨胀性能的影响

    Institute of Scientific and Technical Information of China (English)

    杨晓辉; 卢锦花; 李克智; 张守阳; 杨茜; 曾燮榕

    2012-01-01

    The thermal expansion behavior of 2D-C/C composites and the effect of fatigue loading conditions on the thermal expansion of the composites were studied. The flexural fatigue experiment was made under the stress level of 70% and 90% , cycling times of 104 , 5 X 104 , 1 X 105 and 1.5x10 , and then the thermal behavior was investigated. The results show that fatigue loading didn't change the variation law that thermal expansion behavior is improved with the increased temperature. However, compared with the thermal expansion behavior of 2D-C/C composites at different fatigue loading conditions, the thermal expansion behavior of the samples after fatigue loading drops with increasing of the stress level and cycling times, which is due to the all kinds of fatigue damages generated during the fatigue loading.%研究了2D-C/C复合材料的热膨胀性能以及疲劳加载条件对其热膨胀性能的影响规律,分别进行了应力水平为70%、90%及循环周次为104、5×104、1×105和1.5×105次的弯-弯疲劳试验,并随后测试其热膨胀性能.结果表明,疲劳加载并没有改变其热膨胀性能随温度升高而增大的变化规律,但对比不同疲劳加载条件下2D-C/C复合材料的热膨胀性能,可发现疲劳加载后试样的热膨胀性能随着应力水平和循环周次的增大有降低趋势.经分析认为,这主要是由于疲劳加载过程中产生的各种疲劳损伤所致.

  6. Fatigue reliability for LNG carrier

    Institute of Scientific and Technical Information of China (English)

    Xiao Taoyun; Zhang Qin; Jin Wulei; Xu Shuai

    2011-01-01

    The procedure of reliability-based fatigue analysis of liquefied natural gas (LNG) carrier of membrane type under wave loads is presented. The stress responses of the hotspots in regular waves with different wave heading angles and wave lengths are evaluated by global ship finite element method (FEM). Based on the probabilistic distribution function of hotspots' short-term stress-range using spectral-based analysis, Weibull distribution is adopted and discussed for fitting the long-term probabilistic distribution of stress-range. Based on linear cumulative damage theory, fatigue damage is characterized by an S-N relationship, and limit state function is established. Structural fatigue damage behavior of several typical hotspots of LNG middle ship section is clarified and reliability analysis is performed. It is believed that the presented results and conclusions can be of use in calibration for practical design and initial fatigue safety evaluation for membrane type LNG carrier.

  7. Low-Cycle Fatigue Life and Fatigue Crack Propagation of Sintered Ag Nanoparticles

    Science.gov (United States)

    Shioda, Ryutaro; Kariya, Yoshiharu; Mizumura, Noritsuka; Sasaki, Koji

    2017-02-01

    The low-cycle fatigue life and fatigue crack propagation behavior of sintered silver nanoparticles were investigated using miniature specimens sintered at two different temperatures. The fatigue crack initiation life and fatigue crack propagation rate of sintered Ag nanoparticles were extremely sensitive to changes in the range of inelastic energy density and the cyclic J integral, exhibiting brittle characteristics, in contrast to tin-based lead-free solder alloys. With increasing sintering temperature, the fatigue crack propagation rate decreased. On the other hand, the effect of sintering temperature on the fatigue crack initiation life differed depending on the use of either a smooth specimen (low-cycle fatigue test) or notched specimen (fatigue crack propagation test). For the notched specimens, the probability of grain boundaries around the notch decreased due to increased sintering temperature. Therefore, the fatigue crack initiation life was increased with an increase in sintering temperature in the fatigue crack propagation test. In the smooth specimen, however, the fatigue life decreased with an increase in sintering temperature, as the elastic modulus of the specimen increased with increasing sintering temperature. In the low-cycle fatigue test, the specimen sintered with high internal stress started to develop crack initiation early, causing a decrease in the crack initiation life.

  8. Carbon nanotube reinforced hybrid composites: Computational modeling of environmental fatigue and usability for wind blades

    DEFF Research Database (Denmark)

    Dai, Gaoming; Mishnaevsky, Leon

    2015-01-01

    The potential of advanced carbon/glass hybrid reinforced composites with secondary carbon nanotube reinforcement for wind energy applications is investigated here with the use of computational experiments. Fatigue behavior of hybrid as well as glass and carbon fiber reinforced composites...... with and without secondary CNT reinforcement is simulated using multiscale 3D unit cells. The materials behavior under both mechanical cyclic loading and combined mechanical and environmental loading (with phase properties degraded due to the moisture effects) is studied. The multiscale unit cells are generated...... with the secondary CNT reinforcements (especially, aligned tubes) present superior fatigue performances than those without reinforcements, also under combined environmental and cyclic mechanical loading. This effect is stronger for carbon composites, than for hybrid and glass composites....

  9. Corrosion Fatigue

    Science.gov (United States)

    1981-10-01

    the applied protection systems, (2) crevices for moisture entrapment, (3) galvanic couples when steel or titanium fasteners are used, and (4) fatigue...Activ Material Structure Exposed Normal Environment* Unexposed Atmosphere Aluminum alloys Steel 1.25 2.0 4.0 Titanium " Magnesium " (4.0) (8.0) (10.0...APPRNDIX - Chromic Acid Anodizing The surface treatment consists in the following process : D egreasing with trichlorethylene vapor, * Pickling , Composition

  10. Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic NiTi Ball Bearings

    Science.gov (United States)

    Dellacorte, Christopher; Howard, S. Adam; Thomas, Fransua; Stanford, Malcolm K.

    2017-01-01

    Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

  11. Effects of bionic units on the fatigue wear of gray cast iron surface with different shapes and distributions

    Science.gov (United States)

    Chen, Zhi-kai; Lu, Shu-chao; Song, Xi-bin; Zhang, Haifeng; Yang, Wan-shi; Zhou, Hong

    2015-03-01

    To improve the fatigue wear resistance of gray cast iron (GCI), GCI samples were modified by a laser to imitate the unique structure of some soil animals alternating between soft and hard phases; the hard phase resists the deformation and the soft phase releases the deformation. Using the self-controlled fatigue wear test method, the fatigue wear behaviors of treated and untreated samples were investigated and compared experimentally. The results show that the bionic non-smooth surface obtains a beneficial effect on improving the fatigue wear resistance of a sample, and the fatigue wear resistance of the bionic sample assembled with reticulate units (60°+0°), whose mass loss was reduced by 62%, was superior to the others. Meanwhile, a finite element (FE) was used to simulate the compression and the distributions of strain and stress on the non-smooth surface was inferred. From these results, we understood that the functions of the bionic unit such as reducing strain and stress, and also obstructing the closure and propagation of cracks were the main reasons for improving the fatigue wear property of GCI.

  12. 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)

    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

    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.

  13. Competing fatigue mechanisms in Nickel-base superalloy Rene 88DT

    Science.gov (United States)

    Chang, Paul N.

    Nickel base superalloys exhibit superior high temperature mechanical properties required for aircraft engine components. It has been known that the processing of these alloys by the powder metallurgy route introduces inclusions inside the material. The presence of such inclusions often leads to competing failure modes in fatigue that is described by a step-wise or two distinct S-N curves involving both the surface and internally-initiated cracks, resulting in large uncertainties of fatigue life. A clear understanding of such behavior is yet to be established. The principal objective of this research is to examine the effect of inclusions on the extent of fatigue failure competition from surface and internal initiators at two different specimen test volumes. Experimental fatigue testing has been performed to explore how the presence of inclusions affects the competing fatigue failure modes. In addition, how the competing failure modes will behave with changes in the specimen size was also studied. Two groups of material each with two different specimen sizes were used in this study. It has been shown that the two crack initiation mechanisms occurred in the small unseeded Rene 88DT specimens tested at 650ºC over the stress range tested. Additionally, the fatigue lives were reduced with increase in specimen volume. All fatigue failures in seeded material occurred due to crack initiations from the seeded inclusions. In the fatigue life of seeded material, two competing and separate S-N curves were found in small test volume, whereas, in the large test volume, the regions were separated by a "step" in S-N curve. It has been found that the largest inclusion size observed in metallographic surfaces was smaller than the size determined from the fatigue failure origin. An analysis method based on extreme value statistics developed by Murakami was used to predict the largest size of inclusion in the test volume. The results of this study clearly show that competition for

  14. Estudio experimental sobre el comportamiento del hierro austemperado nitrurado (adi a la fatiga de contacto. // Experimental study to contact fatigue behavior of nitrided-austempered ductile iron.

    Directory of Open Access Journals (Sweden)

    C. Figueroa

    2001-10-01

    Full Text Available En el presente trabajo se muestra un estudio sobre el hierro fundido austemperado nitrurado sometido a pruebas de fatiga decontacto. El mismo se austenitizó y austemperó a las temperaturas de 900 y 3800C respectivamente, seleccionándose enambos casos un tiempo de 2 horas. Después se le aplicó un proceso de nitruración gaseosa a 5700C durante 6 horas.Las experiencias fueron realizadas en una máquina para el ensayo de fatiga de contacto con discos. Las presionesHertzianas utilizadas fueron de 1.73, 1.78, 2.04, 2.41, 2.46 y 2.71 GPa.La composición de fases se determinó utilizando la difracción de rayos X, evidenciándose la presencia de los compuestos e(Fe2-3N y g¢ (Fe4N. Los defectos tales como: pittings spalls y grietas fueron observados por medio de la microscopíaelectrónica de barrido (SEM. Los resultados indicaron que la capa nitrurada entre 5 y 6 micras de espesor desaparece bajola acción de las presiones de contacto. Por otra parte se pudo detectar una disminución de la resistencia a la fatiga en el ADInitrurado cuando fueron utilizadas bajas presiones Hertzianas También se comprobó que los nódulos de grafito actúancomo barreras a la propagación de grietas.Palabras claves: Fatiga de contacto, Capa nitrurada, hierro dúctil austemperado, máquina de fatiga condiscos, rayos X._____________________________________________________________________AbstractThis paper presents a study on the behavior of nitrided austempered ductile iron (ADI under contact fatigue tests. ADI wasaustenitized at 9000C for 2 hours and austempered at 380oC for 2 hours. Later, the ADI was nitrided at 570oC for a periodof 6 hours.The contact fatigue tests were carried out using a disc test machine. Hertzian pressures of 1.73, 1.78, 2.04, 2.41, 2.46 and2.71 were used during the tests.The phase composition of nitride layer was determined using X-ray analysis, which detected the presence of the e and g¢phases. The pitting, spalls and cracks that appeared

  15. A conceptual framework for interpretation of MMC fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Talreja, R. [Georgia Inst. of Tech., Atlanta (United States). School of Aerospace Engineering

    1995-09-01

    A previously developed conceptual framework for interpretation of fatigue of polymer matrix composites (PMCs) is revisited for the purpose of the interpretation of fatigue in metal matrix composites (MMCs). With appropriate modifications, the basic features in the mechanisms based fatigue life diagrams of PMCs are found to hold for MMCs as well. Fatigue data for different MMC systems are examined with the interpretative framework and some observed trends are clarified. Approaches to fatigue life modeling are discussed for the different regions of behavior interpreted by the fatigue life diagram concept. (orig.)

  16. ACTITUDES Y COMPORTAMIENTO LECTOR: UNA APLICACIÓN DE LA TEORÍA DE LA CONDUCTA PLANEADA EN ESTUDIANTESDE NIVEL MEDIO SUPERIOR/ ATTITUDES AND READER BEHAVIOR: AN APPLICATION OF THE THEORY OF PLANNED BEHAVIOR OF STUDENTS IN UPPER INTERMEDIATE LEVEL

    Directory of Open Access Journals (Sweden)

    Serafín Joel Mercado Doménech***

    2011-02-01

    Full Text Available RESUMENEl objetivo de la presente investigación fue determinar la influencia de los componentes de la teoría de la conductaplaneada sobre indicadores del comportamiento lector en estudiantes mexicanos de nivel medio superior. Con una muestraconstituida por 305 estudiantes, los resultados de los análisis de ecuaciones estructurales mostraron índices que sugierenel poco ajuste del modelo como estructura explicativa general de los indicadores del comportamiento lector considerados eneste estudio. Con algunas adecuaciones basadas en las pruebas de multiplicadores de Lagrange y de Wald, un segundoanálisis indicó el ajuste satisfactorio de las variables del modelo de la conducta planeada a los indicadores del comportamientolector, siendo las principales variables explicativas la actitud en sus componentes afectivo y cognitivo. Los resultados sondiscutidos respecto a las implicaciones teóricas y consecuencias educacionales en relación al impacto que las actitudespueden tener en el fomento de esta actividad.ABSTRACTThe objective of this research was to determine the influence of the components of the theory of planned behavior onindicators of reading behavior in Mexican students high school level. With a sample consisting of 305 students, the resultsof structural equation modeling showed fit indices that suggest the inadequacy of the model as general explanatorystructure of the indicators of reading behavior in this study. With some adjustments based on the tests of Lagrangemultipliers and Wald, a second analysis indicated the adjustment of the variables of the model of planned behavior toindicators of reading behavior, the main explanatory variables attitude on affective and cognitive components. The resultsare discussed regarding the theoretical implications and educational implications regarding the impact that attitudes canhave in promoting this activity.

  17. Fatigue of Dental Implants: Facts and Fallacies

    Directory of Open Access Journals (Sweden)

    Keren Shemtov-Yona

    2016-05-01

    Full Text Available Dental implants experience rare yet problematic mechanical failures such as fracture that are caused, most often, by (time-dependent metal fatigue. This paper surveys basic evidence about fatigue failure, its identification and the implant’s fatigue performance during service. We first discuss the concept of dental implant fatigue, starting with a review of basic concepts related to this failure mechanism. The identification of fatigue failures using scanning electron microscopy follows, to show that this stage is fairly well defined. We reiterate that fatigue failure is related to the implant design and its surface condition, together with the widely varying service conditions. The latter are shown to vary to an extent that precludes devising average or representative conditions. The statistical nature of the fatigue test results is emphasized throughout the survey to illustrate the complexity in evaluating the fatigue behavior of dental implants from a design perspective. Today’s fatigue testing of dental implants is limited to ISO 14801 standard requirements, which ensures certification but does not provide any insight for design purposes due to its limited requirements. We introduce and discuss the random spectrum loading procedure as an alternative to evaluate the implant’s performance under more realistic conditions. The concept is illustrated by random fatigue testing in 0.9% saline solution.

  18. Low cycle fatigue of irradiated LMFBR materials

    Energy Technology Data Exchange (ETDEWEB)

    Blackburn, L D

    1976-01-01

    A review of low cycle fatigue data on irradiated LMFBR materials was conducted and extensive graphical representations of available data are presented. Representative postirradiation tensile properties of annealed 304 and 316 SS are selected and employed in several predictive methods to estimate irradiated material fatigue curves. Experimental fatigue data confirm the use of predictive methods for establishing conservative design curves over the range of service conditions relevant to such CRBRP components as core former, fixed radial shielding, core barrel, lower inlet module and upper internals structures. New experimental data on fatigue curves and creep-fatigue interaction in irradiated 20 percent cold worked (CW) 316 SS and Alloy 718 would support the design of removable radial shielding and upper internals in CRBRP. New experimental information on notched fatigue behavior and cyclic stress-strain curves of all these materials in the irradiated condition could provide significant design data.

  19. Low-cycle Fatigue Behavior of Permanent-mold Cast Al-Si-Cu-Er Alloy%金属型铸造Al-Si-Cu-Er合金的低周疲劳行为

    Institute of Scientific and Technical Information of China (English)

    吴伟; 王爽; 吕伟; 车欣

    2011-01-01

    通过在不同外加总应变幅下进行应变控制的室温低周疲劳试验,探讨了金属型铸造A1-Si-Cu-Er合金的疲劳变形和断裂行为.结果表明,在低周疲劳加载下,金属型铸造Al-Si-Cu-Er合金表现为循环应变硬化、循环稳定;金属型铸造Al-Si-Cu-Er合金的弹性应变幅、塑性应变幅与疲劳断裂时的载荷反向周次之间的关系可分别用Basquin和Coffin-Manson公式描述;金属型铸造Al-Si-Cu-Er合金在低周疲劳加载条件下,裂纹均以穿晶方式萌生于试样表面,并以穿晶方式扩展.%The fatigue deformation and fracture behavior of permanent-mold cast Al-Si-Cu-Er alloy were investigated by low-cycle fatigue test at room temperature under different total strain amplitudes. The results show that permanent-mold cast Al-Si-Cu-Er alloy exhibits cyclic strain hardening and stable cyclic stress response during fatigue deformation, which mainly depend on the imposed total strain. The relation between elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by Coffin-Manson and Basquin equations,respectiveiy. In addition, the fatigue cracks initiate at the free surface of fatigue specimens and propagate in a transgranular mode under low-cycle fatigue.

  20. Automotive stamped part fatigue design

    Directory of Open Access Journals (Sweden)

    Caudoux Mélanie

    2014-06-01

    Full Text Available Fatigue design of automotive axle parts is of prior concern because of these are high safety parts and they are expected to drive the overall vehicle mass reduction. In this framework, the stamping process is widely used to form axle parts, before assembling them by welding. Consequently, the mechanical and physical characteristics of the blank sheet are modified, having a strong influence on the fatigue behavior. In this paper, we address the consequences of the stamped process on the fatigue design and how they may be effectively taken into account in the automotive industry. Actually, the coupling between the stamping process and the fatigue design is under development at PSA Peugeot Citroën Company since several years. Such an analysis deals with some major topics: thickness variation, plastic hardening and deformation, and residual stress. All of these ingredients result in fatigue criteria evolutions: it is important to stress that the stamping process can have advantageous or disadvantageous consequences on the fatigue design. This is here highlighted on some examples, dealing with front and rear axles.

  1. Cancer-Related Fatigue and Rehabilitation : A Randomized Controlled Multicenter Trial Comparing Physical Training Combined With Cognitive-Behavioral Therapy With Physical Training Only and With No Intervention

    NARCIS (Netherlands)

    van Weert, E.; May, A.M.; Korstjens, I.; Post, W.J.; van der Schans, C.P.; van den Borne, B.; Mesters, I.; Ros, W.J.G.; Hoekstra-Weebers, J.E.H.M.

    2010-01-01

    Background. Research suggests that cancer rehabilitation reduces fatigue in survivors of cancer. To date, it is unclear what type of rehabilitation is most beneficial. Objective. This randomized controlled trial compared the effect on cancer-related fatigue of physical training combined with cogniti

  2. Cancer-related fatigue and rehabilitation: A randomized controlled multicenter trial comparing physical training combined with cognitive-behavioral therapy with physical training only and with no intervention

    NARCIS (Netherlands)

    E. van Weert (Ellen); A.M. May (Anne); I. Korstjens (Irene); W.J. Post (Wendy); C.P. van der Schans (Cees); B. van den Borne (Bart); I. Mesters (Ilse); W.J.G. Ros (Wynand); J.E.H.M. Hoekstra-Weebers (Josette)

    2010-01-01

    textabstractBackground. Research suggests that cancer rehabilitation reduces fatigue in survivors of cancer. To date, it is unclear what type of rehabilitation is most beneficial. Objective. This randomized controlled trial compared the effect on cancerrelated fatigue of physical training combined

  3. Cancer-Related Fatigue and Rehabilitation : A Randomized Controlled Multicenter Trial Comparing Physical Training Combined With Cognitive-Behavioral Therapy With Physical Training Only and With No Intervention

    NARCIS (Netherlands)

    van Weert, E.; May, A.M.; Korstjens, I.; Post, W.J.; van der Schans, C.P.; van den Borne, B.; Mesters, I.; Ros, W.J.G.; Hoekstra-Weebers, J.E.H.M.

    2010-01-01

    Background. Research suggests that cancer rehabilitation reduces fatigue in survivors of cancer. To date, it is unclear what type of rehabilitation is most beneficial. Objective. This randomized controlled trial compared the effect on cancer-related fatigue of physical training combined with

  4. Cancer-related fatigue and rehabilitation: A randomized controlled multicenter trial comparing physical training combined with cognitive-behavioral therapy with physical training only and with no intervention

    NARCIS (Netherlands)

    E. van Weert (Ellen); A.M. May (Anne); I. Korstjens (Irene); W.J. Post (Wendy); C.P. van der Schans (Cees); B. van den Borne (Bart); I. Mesters (Ilse); W.J.G. Ros (Wynand); J.E.H.M. Hoekstra-Weebers (Josette)

    2010-01-01

    textabstractBackground. Research suggests that cancer rehabilitation reduces fatigue in survivors of cancer. To date, it is unclear what type of rehabilitation is most beneficial. Objective. This randomized controlled trial compared the effect on cancerrelated fatigue of physical training combined w

  5. MANAGING FATIGUE IN SPORTS

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ Fatigue is a multifactorial process. Depletion of energy sources, including adenosine triphosphate (ATP), phosphocreatine (PCr), plus carbohydrates (CHO) like muscle glycogen and blood glucose can contribute to fatigue.

  6. Thermal Fatigue Behavior of Silicon-Carbide-Doped Silver Microflake Sinter Joints for Die Attachment in Silicon/Silicon Carbide Power Devices

    Science.gov (United States)

    Zhang, Hao; Chen, Chuantong; Nagao, Shijo; Suganuma, Katsuaki

    2017-02-01

    We studied the thermal fatigue behavior of submicron silicon carbide particle (SiCp)-doped silver (Ag) microflake sinter joints for die attachment in next-generation power devices. Si dummy chips and direct bonded copper substrates with various metallization schemes were bonded using SiCp-doped Ag microflakes under mild conditions (250°C, 30 min, 0.4 MPa). The SiCp was distributed homogeneously in the porous Ag network and inhibited morphological evolution during thermal cycling tests. The shear strength of as-sintered pure Ag and SiCp-added joints was ˜50 MPa and 35 MPa, respectively. Thermal cycling tests from -40°C to 250°C were conducted for up to 1000 cycles (hours) to characterize the thermostability of the bonded joints. After 1000 cycles, joints with and without SiCp experienced bonding degradation, with shear strength of ˜25 MPa and 20 MPa, respectively. Thus, after 1000 cycles, the shear strength of pure Ag and SiCp-doped joints decreased by 58% and 42%, respectively, compared with their maximum value. Coarsening of porous Ag occurred in pure Ag joints. SiCp addition inhibited morphological evolution of SiCp-doped joints during thermal cycling. However, vertical cracks generated by thermal stress were observed in joints both with and without SiCp, which may limit long-term reliability.

  7. STUDY ON FATIGUE CRACK GROWTH BEHAVIOR OF 16MnR STEEL UNDER DIFFERENT CONDITIONS%16MnR钢在不同条件下的疲劳裂纹扩展规律

    Institute of Scientific and Technical Information of China (English)

    熊缨; 陈冰冰; 郑三龙; 高增梁

    2009-01-01

    采用压力容器用16MnR热轧钢不同缺口尺寸、不同厚度的紧凑拉伸(CT)试样,进行了不同温度、不同应力比条件的一系列疲劳裂纹扩展实验,得到了相应实验条件下的疲劳裂纹扩展速率.讨论了高温环境、缺口半径,应力比及试样厚度对疲劳裂纹扩展行为的影响规律.结果表明:16MnR钢在环境温度为150和300℃时的疲劳裂纹扩展速率比25和425℃时低,300℃时疲劳裂纹扩展速率最低,300℃以上时随温度的升高裂纹扩展速率增大;缺口半径的大小对初期疲劳裂纹扩展有较大的影响;应力比对16MnR钢的疲劳裂纹扩展行为没有影响;疲劳裂纹扩展速率随试样厚度的增大而增大.%16MnR steelis a most widely used material for pressure vessels.The study on fatigue is very important for safety and fatigue life assessment of pressure vessels.Several experimental researches for fatigue of 16MnR steel were conducted and test data have been gotten,but it was short of fatigue study of the material under various conditions at present.The fatigue crack growth tests of 16MnR hot-rolling steel were carried out at different temperatures and R-ratios with compact tension(CT)specimens in this paper.Different sized circular notches at the tip of the slot ranging from very sharp to blunt were used in the CT specimens and the radii of the notches were 0.1,1 and 2 mm,and the thicknesses of CT specimens were 3.8,12.5,18 and 25 mm,respectively.The fatigue crack growth performances were obtained.The effects of temperatures,notch sizes,R-ratios and specimen thickness on fatigue crack growth behaviors were studied.It was shown that the fatigue crack growth rates at 150 and 300℃were lower than those at 25 and 425℃.the lowest one was at 300℃ and the crack growth rate increased with temperature above 300℃.The great influence of notch sizes on the fatigue crack growth rate was observed at early stage of crack growth only.The results also indicated

  8. Study of fatigue behaviour of 7475 aluminium alloy

    Indian Academy of Sciences (India)

    B B Verma; J D Atkinson; M Kumar

    2001-04-01

    Fatigue properties of a thermomechanically treated 7475 aluminium alloy have been studied in the present investigation. The alloy exhibited superior fatigue life compared to conventional structural aluminium alloys and comparable stage II crack growth rate. It was also noticed that the fatigue crack initiated from a surface grain and the crack extension was dominated by ductile striations. Analysis also revealed that this alloy possessed fracture toughness and tensile properties superior to that noticed with other structural aluminium alloys. Therefore the use of this alloy can safely reduce the overall weight of the aircraft.

  9. Temperament vs. chronic fatigue in police officers

    Directory of Open Access Journals (Sweden)

    Ewa Stępka

    2015-12-01

    Full Text Available Background: Chronic fatigue is a problem affecting a still growing number of people. Among them there are representatives of different professions who are forced to cope not only with occupational stress, but also with the problem of fatigue. The police is one of such occupational groups, in which exposure to stressful and often traumatic situations, contact with those who violate the law, shift work and contact with superiors can play a key role in the development of chronic fatigue. However, chronic fatigue, induced by the above mentioned factors, does not affect all police officers since its occurrence also depends on many personal traits, including temperament. Material and methods: We studied a group of 61 police officers of the Kuyavian-Pomeranian garrison. The study was conducted using the Buss and Plomin EAS (emotionality, activity, sociability Temperament Questionnaire, CIS-20R (community, innovation, survey Questionnaire, developed by Vercoulen et al. and a questionnaire on socio-demographic data. Results: The results indicated the relationship between chronic fatigue and emotionality. Statistical analyses showed a negative correlation between the nature of emotional components, distress, fear, anger, and the general rate of chronic fatigue. There was no statistically significant correlation between age, and service experience and the level of chronic fatigue. Conclusions: The results indicate that the officers of the study group show dramatically high levels of chronic fatigue. The results also revealed that temperament characteristics, such as sociability and activity, reported in the literature as factors reducing fatigue and stress, did not show relevance to chronic fatigue in the study group. Med Pr 2015;66(6:793–801

  10. Effect of higher strain range cycling on near fatigue-limit fatigue life

    Energy Technology Data Exchange (ETDEWEB)

    Fukuoka, Chie; Nakagawa, Y.G. [Ishikawajima-Harima Heavy Industries Co. Ltd., Tokyo (Japan). Research Inst; Rosinski, S.T.

    1999-04-01

    The objective of this study is to clarify the effects of pre-cycling above the fatigue limit on near the fatigue-limit fatigue behaviors of SA508, low alloy steel for nuclear pressure vessels, correlating fatigue lifetime with microstructural changes in the bulk. It has been observed that dislocation cell structure is well developed in an as-received SA508 sample and the misorientation among cells increases with fatigue accumulation during fatigue tests. The cell to cell misorientation was measured and statistically quantified by the Selected Area electron beam Diffraction (SAD). It was shown that a fatigue crack started growing abruptly when the SAD value (the mean misorientation among cells) exceeded a critical angle, 4-5 degrees. Fatigue tests were performed for SA508 samples, first at a high total strain range (0.62%) to 10, 100, and 6000 cycles followed by cycling at near the fatigue-limit strain range (0.40%). The sample with pre-cycling for 100 and 6000 cycles failed while ones with pre-cycling for 10 cycles and without pre-cycling did not rupture till about 10{sup 6} cycles where the tests were terminated. Small surface cracks were found all samples pre-cycled at the high strain range but the cracks were arrested for a long time at the near fatigue limit cycling followed by an abrupt growth at the failure. It was found by the SAD that samples failed at the fatigue limit when the average misorientation among cells exceeds the critical angle regardless of pre-cycling histories. The SAD value changed even during cycling below the fatigue limit, and the change in SAD value was strongly influenced by the number of pre-cycling above the fatigue limit. These changes well agreed with fatigue lifetime of the samples. (author)

  11. Standard guide for fretting fatigue testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This guide defines terminology and covers general requirements for conducting fretting fatigue tests and reporting the results. It describes the general types of fretting fatigue tests and provides some suggestions on developing and conducting fretting fatigue test programs. 1.2 Fretting fatigue tests are designed to determine the effects of mechanical and environmental parameters on the fretting fatigue behavior of metallic materials. This guide is not intended to establish preference of one apparatus or specimen design over others, but will establish guidelines for adherence in the design, calibration, and use of fretting fatigue apparatus and recommend the means to collect, record, and reporting of the data. 1.3 The number of cycles to form a fretting fatigue crack is dependent on both the material of the fatigue specimen and fretting pad, the geometry of contact between the two, and the method by which the loading and displacement are imposed. Similar to wear behavior of materials, it is important t...

  12. Fatigue life extension

    Science.gov (United States)

    Matejczyk, D. E.; Lin, J.

    1985-01-01

    Potential fatigue rejuvenation processes were carried out on fatigue-damaged material both with and without observable surface-connected fatigue cracks. The fatigue life of fatigue-damaged MAR-M246(Hf)(DS), a directionally solidified nickel-base superalloy used in turbine airfoils, was extended by reheat treatment. The fatigue life of fatigue-cracked Inconel 718, a wrought nickel-base superalloy used in a wide variety of advanced rocket engine components, was extended by electron-beam welding to close off the surface-connected crack, followed by hot isostatic pressing and reheat treatment.

  13. 不同片层组织对TC4-DT钛合金裂纹扩展行为的影响%Influence of Lamellar Microstructure on Fatigue Crack Propagation Behavior of TC4-DT of Damage Tolerance

    Institute of Scientific and Technical Information of China (English)

    祝力伟; 朱知寿; 王新南; 曹春晓

    2011-01-01

    The effects of lamellar microstructure on fatigue crack propagation behavior of damage tolerance for TC4-DT alloy plate were studied. Lamellar microstructure of TC4-DT alloy plate was obtained using different β heat treatment. Fatigue crack growth rate with fine and coarse lamellar structure were characterized. The experimental results show that in near threshold and low growth region of Paris region, microstructure with coarse lamellar has tremendous influence to the fatigue crack growth rate; Microstructure with fine lamellar structure had a lower fatigue crack growth rate and flexuous crack propagating route in the lamellar microstructure compared with the coarse lamellar structure. With the increasing of lamellar thickness, fatigue crack growth rate accelerated. In order to achieve an excellent damage tolerance, it is necessary to obtain fine lamellar structure with near β heat treatment by controlling the parameter strictly.%采用三种β热处理制度对TC4-DT钛合金板材进行热处理,调整合金的显微组织和损伤容限性能.利用金相显微镜对不同热处理制度下合金的片层组织特征参数进行观察,分析了不同片层组织对合金疲劳裂纹扩展速率的影响.结果表明,粗片层组织的疲劳裂纹扩展速率在近门槛区对组织比较敏感;在Paris区,细片层组织具有较低的疲劳裂纹扩展速率,随着片层厚度的增加,裂纹扩展速率加快;合金在β区短时保温具有更好的综合性能.

  14. 纳米晶Ni疲劳行为的实验研究%EXPERIMENTAL INVESTIGATION ON FATIGUE BEHAVIOR OF NANOCRYSTALLINE NICKEL

    Institute of Scientific and Technical Information of China (English)

    谢季佳; 洪友士

    2009-01-01

    系统研究了纳米晶Ni与粗晶Ni的疲劳行为.通过疲劳实验获得了这2种材料的疲劳应力-寿命曲线,并采用AFM对纳米晶Ni样品表面进行观察以研究其裂纹萌生的微观机制,利用纳米压痕仪对疲劳实验前后样品的力学性能和显微组织变化进行了研究.结果表明,纳米晶Ni具有比粗晶Ni更高的疲劳极限.AFM观察表明,纳米晶疲劳后样品表面出现平均尺寸为73 nm的胞状起伏,疲劳后样品的晶粒尺寸未发生明显改变.压痕硬度结果表明,疲劳过程材料的力学性能也未发生明显变化.%Electrodeposited nanocrystalline (nc)metal is often used as a model material in nc material investigation.But electrodeposition typically yields only thin foils that are at most several hundred micrometers in thickness,this arouses experimental difficulties in fatigue testing.There are several investigations on fatigue of electrodeposited nc metals.However,for the lack of direct ex-perimental evidence,the mechanism of fatigue crack nucleation for nc materials is still not clear.In addition to fatigue properties,the microstructure stability is another key point for the practice of bulk nc materials.Some research papers indicated that the grains of nc metal would grow up under quasi-static loading,but no any investigation give out results under cyclic loading.In this paper,fatigue of electrodeposited nc Ni was experimentally investigated.Fatigue testing was carried out to obtain the S-N curves.For the reason that surface is the most important site for fatigue crack initiation ,atomic force microscopy(AFM)was used to scan the sample surface before and after fatigue testing, which provides a direct observation on fatigue crack nucleation mechanism.For investigation on the stability of microstructure,the AFM was also used to measure the grain size of samples after fatigue loading,and nanoindenter was used to investigate the change of mechanical properties of samples af- ter fatigue

  15. Microstructure and fatigue behaviors of a biomedical Ti–Nb–Ta–Zr alloy with trace CeO{sub 2} additions

    Energy Technology Data Exchange (ETDEWEB)

    Song, Xiu [The Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China); Wang, Lei, E-mail: wanglei@mail.neu.edu.cn [The Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China); Niinomi, Mitsuo; Nakai, Masaaki [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Liu, Yang; Zhu, Miaoyong [The Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials and Metallurgy, Northeastern University, Shenyang 110004 (China)

    2014-12-01

    The new β-type Ti–29Nb–13Ta–4.6Zr (TNTZ) alloy containing trace amounts of CeO{sub 2} additions has been designed as a biomedical implant with improved fatigue properties achieved by keeping Young's modulus to a low value. The results show that the microstructure is refined by the addition of CeO{sub 2}; the β grain size becomes a little larger when Ce content increases from 0.05% to 0.10%. This occurs because dispersed CeO{sub 2} particles can act as nucleation sites for β grains; thus, the effect of rare earth oxides on microstructure refinement mainly depends on the size and dispersion of the rare earth oxides. Young's moduli of TNTZ with CeO{sub 2} additions are maintained as low as those of TNTZ without CeO{sub 2}, while the fatigue limit is highly improved. The 0.10% Ce alloy exhibits the best fatigue strength among the experimental alloys; its fatigue strength is increased by 66.7% compared to that of pure TNTZ. The mechanism by which rare earth oxides affect fatigue performance is dominated by dispersion strengthening. The stiff rare earth oxides can hinder the movement of dislocations, resulting in resistance to the formation of fatigue cracks. Rare earth oxides also change the crack propagation direction and the crack propagation route, effectively decreasing the crack propagation rate.

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

    Energy Technology Data Exchange (ETDEWEB)

    Keisler, J.; Chopra, O.K.; Shack, W.J. [Argonne National Lab., IL (United States)

    1995-08-01

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

  17. The Influence of Microcleanliness on the Fatigue Performance of Nitinol

    Science.gov (United States)

    Kumar, Parikshith K.; Lasley, Christopher

    2014-07-01

    The presence of carbide and oxide inclusions in nitinol, and their influence on the fatigue performance, has been an important consideration in the medical device community. Microcleanliness, as determined by inclusion size and inclusion density, has often been cited as a potential factor influencing the fatigue behavior of the material. However, no comprehensive study has been conducted to determine their impacts on the fatigue behavior. The objective of this effort was to understand the influence of the inclusions present in the material on the fatigue behavior.

  18. 钢板-混凝土组合受弯加固梁疲劳性能试验研究%Experimental research on fatigue behavior of RC beams strengthened by steel plate-concrete composite technique

    Institute of Scientific and Technical Information of China (English)

    聂建国; 王宇航

    2011-01-01

    Based on fatigue experiments on eight RC beams strengthened by steel plate-concrete composite (SPCC) technique, fatigue life and variation trend of strain under constant amplitude fatigue loading were studied.The experimental results show that the fatigue failure mode of steel plate-concrete composite beam is fatigue failure of the steel plates.The initial fatigue crack in steel plates appears near the welded toe of stud and then expansion though.But different from general RC beams, the fatigue failure mode of specimens is ductile.Amplitude of stress in steel plate has most important influence on fatigue behavior of RC beams strengthened by SPCC technique.Level and amplitude of stress in steel plate should be controlled strictly in practical design and high strength steel and thin steel plate are not suitable for RC beams strengthened by SPCC technique.The pre-stress in steel plate can improve fatigue life of RC beams strengthened by SPCC technique.The S-N relation for tension steel plate welded with studs provided in ' Code for railway steel bridges design' is safe enough for the design of steel plates in RC beams strengthened by SPCC technique.The calculational method for fatigue life is proposed considering effects of stress level and stress amplitude.%通过对8根钢板-混凝土组合受弯加固简支梁(以下简称组合加固梁)的等幅疲劳加载试验,研究了组合加固梁在疲劳荷载作用下的寿命及应变变化规律.试验结果表明:组合加固梁的疲劳破坏是由钢板裂纹从栓钉焊趾处开始缓慢扩展直至贯通导致的,与普通钢筋混凝上梁相比,组合加固梁的疲劳破坏具有较好的延性;钢板应力幅对组合加同梁的疲劳性能影响较大,实际设计时应严格控制钢板的应力幅和应力上限,不宜采用高强钢材和较薄的钢板;加固层预应力可有效提高组合加固梁的疲劳性能;按TB 10002.2-2005中规定的焊有栓钉的受拉钢板的S-N关系对钢板-混凝

  19. On the Fatigue Analysis of Wind Turbines

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, Herbert J.

    1999-06-01

    Modern wind turbines are fatigue critical machines that are typically used to produce electrical power from the wind. Operational experiences with these large rotating machines indicated that their components (primarily blades and blade joints) were failing at unexpectedly high rates, which led the wind turbine community to develop fatigue analysis capabilities for wind turbines. Our ability to analyze the fatigue behavior of wind turbine components has matured to the point that the prediction of service lifetime is becoming an essential part of the design process. In this review paper, I summarize the technology and describe the ''best practices'' for the fatigue analysis of a wind turbine component. The paper focuses on U.S. technology, but cites European references that provide important insights into the fatigue analysis of wind turbines.

  20. Bending Fatigue Damage Behavior of Bearing Wire Rope on Different Pre-tension%承载钢丝绳在不同预张力下的弯曲疲劳损伤研究

    Institute of Scientific and Technical Information of China (English)

    贾小凡; 张德坤

    2011-01-01

    以6×19+FC点接触式钢丝绳为研究对象,研究钢丝绳在不同预张力下的弯曲疲劳损伤行为,考察不同预张力对弯曲疲劳寿命、损伤量值、外层可见断丝数和钢丝之间的微动磨损的影响,探索其疲劳损伤机制.在自制的钢丝绳弯曲疲劳试验机上开展钢丝绳在不同预张力下的弯曲疲劳试验,采用钢丝绳无损检测仪和人工检测方法分别判定不同预张力下钢丝绳的弯曲疲劳寿命,采用光学显微镜和扫描电镜观察分析钢丝绳的疲劳损伤机制.结果表明,钢丝绳的弯曲疲劳寿命随着预张力的增大而减小,其损伤量值和外层可见断丝数随着弯曲疲劳次数的增加而增大,断丝均发生在外层钢丝与弯曲滑轮磨损严重处,断丝长度有集中现象;其疲劳断裂机理表明,钢丝绳内部钢丝之间的微动磨损亦是影响钢丝绳疲劳寿命的重要因素.%The 6Χ 19+FC point contact rope is taken as the research object to study the bending fatigue behavior of the hoisting rope. The influence of the pre-tension to the bending fatigue life, the damage value and the number of the visible broken wires is investigated to explore the fatigue damage mechanism. The effect of the pre-tension on the bending fatigue behavior is tested by the test carried out on the self-made bending fatigue apparatus. Wire rope nondestructive testing instrument and manual inspection are used to detect the bending fatigue life, respectively. Furthermore, the morphologies of the fatigue damaged steel wire surfaces are observed on the optical electron microscope and the S-3000N scanning electron microscope. The results show that, the damage value and the number of the visible broken wires in the outer layer increase with the increase of pre-tension while the bending fatigue life of the wire rope decrease. The broken wires appear at the position of the outer layer where wear seriously with the bending pulleys. Moreover, broken wires appear

  1. Fast prediction of the fatigue behavior of short-fiber-reinforced thermoplastics based on heat build-up measurements: application to heterogeneous cases

    Science.gov (United States)

    Serrano, Leonell; Marco, Yann; Le Saux, Vincent; Robert, Gilles; Charrier, Pierre

    2017-09-01

    Short-fiber-reinforced thermoplastics components for structural applications are usually very complex parts as stiffeners, ribs and thickness variations are used to compensate the quite low material intrinsic stiffness. These complex geometries induce complex local mechanical fields but also complex microstructures due to the injection process. Accounting for these two aspects is crucial for the design in regard to fatigue of these parts, especially for automotive industry. The aim of this paper is to challenge an energetic approach, defined to evaluate quickly the fatigue lifetime, on three different heterogeneous cases: a classic dog-bone sample with a skin-core microstructure and two structural samples representative of the thickness variations observed for industrial components. First, a method to evaluate dissipated energy fields from thermal measurements is described and is applied to the three samples in order to relate the cyclic loading amplitude to the fields of cyclic dissipated energy. Then, a local analysis is detailed in order to link the energy dissipated at the failure location to the fatigue lifetime and to predict the fatigue curve from the thermomechanical response of one single sample. The predictions obtained for the three cases are compared successfully to the Wöhler curves obtained with classic fatigue tests. Finally, a discussion is proposed to compare results for the three samples in terms of dissipation fields and fatigue lifetime. This comparison illustrates that, if the approach is leading to a very relevant diagnosis on each case, the dissipated energy field is not giving a straightforward access to the lifetime cartography as the relation between fatigue failure and dissipated energy seems to be dependent on the local mechanical and microstructural state.

  2. Fast prediction of the fatigue behavior of short-fiber-reinforced thermoplastics based on heat build-up measurements: application to heterogeneous cases

    Science.gov (United States)

    Serrano, Leonell; Marco, Yann; Le Saux, Vincent; Robert, Gilles; Charrier, Pierre

    2017-03-01

    Short-fiber-reinforced thermoplastics components for structural applications are usually very complex parts as stiffeners, ribs and thickness variations are used to compensate the quite low material intrinsic stiffness. These complex geometries induce complex local mechanical fields but also complex microstructures due to the injection process. Accounting for these two aspects is crucial for the design in regard to fatigue of these parts, especially for automotive industry. The aim of this paper is to challenge an energetic approach, defined to evaluate quickly the fatigue lifetime, on three different heterogeneous cases: a classic dog-bone sample with a skin-core microstructure and two structural samples representative of the thickness variations observed for industrial components. First, a method to evaluate dissipated energy fields from thermal measurements is described and is applied to the three samples in order to relate the cyclic loading amplitude to the fields of cyclic dissipated energy. Then, a local analysis is detailed in order to link the energy dissipated at the failure location to the fatigue lifetime and to predict the fatigue curve from the thermomechanical response of one single sample. The predictions obtained for the three cases are compared successfully to the Wöhler curves obtained with classic fatigue tests. Finally, a discussion is proposed to compare results for the three samples in terms of dissipation fields and fatigue lifetime. This comparison illustrates that, if the approach is leading to a very relevant diagnosis on each case, the dissipated energy field is not giving a straightforward access to the lifetime cartography as the relation between fatigue failure and dissipated energy seems to be dependent on the local mechanical and microstructural state.

  3. SHORT FATIGUE CRACK PARAMETER BASED ON THE TOTAL CRACK AREA

    Institute of Scientific and Technical Information of China (English)

    Z.X.Wu; X.C.Wu

    2001-01-01

    The progressive fatigue damage of a material is closely related to the whole populationof cracks on the surface of an un-notched specimen.In order to understand whichparameter is a more useful indicator of fatigue damage,rotatory bending fatigue testswere carried out using smooth specimens of medium-carbon steel.The behavior ofshort crack propagation during fatigue was examined and a new parameter "totalcrack area" was suggested.The aim of this paper is to extend the research on fatiguedamage in the already studied steel and to study how these damage parameters arecorrelated with the process of fatigue damage in order to evaluate the effectiveness ofdamage detection methods.

  4. Effect of Shot Peening Process on Fatigue Behavior of Alloyed Austempered Ductile Iron%喷丸强化对合金化奥贝球铁疲劳性能的影响

    Institute of Scientific and Technical Information of China (English)

    Amir Sadighzadeh Benam; Sasan Yazdani; Behzad Avishan

    2012-01-01

    喷丸处理是改进金属工件疲劳性能最常规的表面处理方法.文中研究了喷丸处理对合金化奥贝球铁(ADI)疲劳性能的影响.等温淬火包括875℃保温90 min奥氏体化处理,然后在320℃、365℃和400℃进行等温处理.用直径0.4~0.6mm的丸喷丸后的试样做旋转弯曲疲劳试验.对试样进行XRD和SEM分析,测定显微硬度和粗糙度,研究试样的疲劳性能.结果表明,在320℃、365℃和400℃等温处理的试样喷丸后疲劳强度分别增加了27.3%、33.3%和48.4%.%Shot peening is one of the most common surface treatments to improve the fatigue behavior of metallic parts. In this study the effect of shot peening process on the fatigue behavior of an alloyed austempered ductile iron (ADI) has been studied. Austempering heat treatment consisted of austenitizing at 875℃ for 90 min and following austempering at 320 ℃, 365 ℃ and 400 ℃. Rotating-bending fatigue test was carried out on samples after shot peening by 0.4 to 0.6 mm shots. XRD and SEM analysis, micro hardness and roughness tests were carried out to study the fatigue behavior of the samples. Results indicate that the fatigue strengths of samples austempered at 320 ℃, 365 ℃ and 400 ℃ are increased by 27.3%, 33.3% and 48.4%, respectively after shot peening process.

  5. 基于低周疲劳损伤的裂纹扩展行为数值模拟新方法%A NEW METHOD OF NUMERICAL SIMULATION FOR BEHAVIOR OF FATIGUE CRACK PROPAGATION BASED ON LOW CYCLE FATIGUE DAMAGE

    Institute of Scientific and Technical Information of China (English)

    黄学伟; 蔡力勋; 包陈; 陈龙

    2011-01-01

    Based on low cycle fatigue critical damage behavior of materials, a numerical simulation method used to predict fatigue crack propagation behavior of materials and structures was presented, and this new method is named as LFF (LCF-Low Cycle Fatigue+FCP-Fatigue Crack Propagation +FEA-Finite Element Analysis). For LFF method, a set of ANSYS command streams for the numerical simulation algorithm were developed to determine the stress and strain amplitude of nodes located at the plastic zone in the direction of crack propagation and fatigue damage of these nodes can be obtained, furtherly, the fatigue crack propagation prediction can be realized by discontinuous crack propagation assumption. For steam turbine rotor material: Cr2Ni2MoV steel, Manson-Coffin critical damage model and Paris crack propagation model of Cr2Ni2MoV steel were obtained by tests on smooth uniaxial specimens and CT (compact tensile) specimens at room temperature respectively. Results show that LFF method has better accuracy to predict fatigue crack propagation behavior of complicated cracks of CT specimens.%基于材料低周疲劳临界损伤,采用应变幅和平均应力定义了一种新的局部疲劳损伤参量,以最大主应变方向的垂直方向作为疲劳裂纹的扩展方向,提出了一种预测材料与结构裂纹在高周疲劳下疲劳裂纹扩展速率的数值模拟新方法:LFF方法(LCF-Low Cycle Fatigue+FCP-Fatigue Crack Propagation +FEA-Finite Element Analysis)。借助有限元分析商业软件,开发了一套命令流程序实现了数值模拟算法,得到裂纹扩展方向上裂尖塑性区域各节点的应力一应变幅,获得每个节点的损伤参数,进而根据疲劳裂纹非连续扩展特性建立疲劳裂纹扩展模型。以大型汽轮机转子材料Cr2Ni2MoV钢为例,通过光滑单轴试样及紧凑拉伸试样试验分别得到了室温低周疲劳临界损伤模型和裂纹扩

  6. Cumulative creep fatigue damage in 316 stainless steel

    Science.gov (United States)

    Mcgaw, Michael A.

    1989-01-01

    The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

  7. Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals

    Directory of Open Access Journals (Sweden)

    Yoshimitsu Okazaki

    2012-12-01

    Full Text Available The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P. grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK than Ti alloy.

  8. Thermal fatigue behavior of niobium microalloyed H13 steel%铌微合金化H13钢的热疲劳行为

    Institute of Scientific and Technical Information of China (English)

    胡心彬

    2006-01-01

    @@ AISI H13 hot work tool steel is widely used for hot forging, hot-extrusion and die-casting because of its high temperature strength, impact toughness, heat checking resistance and wear resistance, etc. The thermally induced surface damage, i. e., thermal fatigue, is believed to be controlled by the magnitude of the imposed cyclic strain. The thermal fatigue on the surface of hot working die, which is responsible to the initiation of the cracks, is reported to result in more than 80 % of the failure of dies.

  9. Thermal Acoustic Fatigue Apparatus

    Data.gov (United States)

    Federal Laboratory Consortium — The Thermal Acoustic Fatigue Apparatus (TAFA) is a progressive wave tube test facility that is used to test structures for dynamic response and sonic fatigue due to...

  10. Insomnia and Fatigue

    Science.gov (United States)

    ... Styles Common Yoga Poses Special Situations Yoga and Lymphedema Risk Yoga and Metastatic Breast Cancer Side Effects ... Insomnia and Fatigue Treatment for Insomnia and Fatigue Lymphedema Lymphedema Risk Treating Lymphedema Menopausal Symptoms Mouth Sores ...

  11. Study of Thermal Fatigue Resistance of a Composite Coating Made by a Vacuum Fusion Sintering Method

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Thermal fatigue behavior of a Ni-base alloy chromium carbide composite coating made by a vacuum fusion sintering method are discussed. Results show that thermal fatigue behavior is associated with cyclic upper temperature and coating thickness. As the thickness of the coating decreases, the thermal fatigue resistance increases. The thermal fatigue resistance cuts down with the thermal cyclic upper temperature rising. The crack growth rate decreases with the increase in cyclic number until crack arrests. Thermal fatigue failure was not found along the interface of the coating/matrix. The tract of thermal fatigue crack cracks along the interfaces of phases.

  12. Optimal Fatigue Testing

    DEFF Research Database (Denmark)

    Faber, M. H.; Sørensen, John Dalsgaard; Kroon, I. B.

    1993-01-01

    This paper considers the reassessment of the reliability of tubular joints subjected to fatigue load. The reassessment is considered in two parts namely the task of utilizing new experimental data on fatigue life to update the reliability of the tubular joint ant the task of planning new fatigue ...

  13. Isothermal Fatigue Behavior of the Near-Eutectic Sn-Ag-Cu Alloy between -25°C and 125°C

    Science.gov (United States)

    Korhonen, Tia-Marje K.; Lehman, Lawrence P.; Korhonen, Matt A.; Henderson, Donald W.

    2007-02-01

    When near-eutectic Sn-Ag-Cu (SAC) alloys are used to make soldered ball-grid-array (BGA) assemblies, the grain size of the joints is very large. During thermomechanical cycling, the solder joint fatigue process is often initiated with recrystallization of the Sn grains, resulting in a smaller grain size in the deformed areas. Grain boundary sliding and increased grain boundary diffusion then results in intergranular crack nucleation and propagation along the recrystallized Sn grain boundaries. In this work, fatigue tests were used to study the initial stages of cyclic deformation damage in Sn-Ag-Cu alloy samples. To separate the solder properties from the constraints introduced by the substrate, the tests were done with free-standing solder specimens, instead of solder joints. The test samples were cast dog-bone specimens that have a cross-sectional diameter of 1 mm, which corresponds to a typical solder joint diameter in BGAs. Mechanical cycling was performed isothermally at several temperatures, from -25°C to 125°C. Typical test conditions were ± 1.5% strain and 15-minute hold at tensile peak stress to allow stress relaxation to take place. Optical microscopy, scanning electron microscopy, and electron backscattering diffraction were used to study the microstructures of the samples before and after fatigue testing in order to obtain insight into the nucleation and growth mechanisms of fatigue damage.

  14. 疲劳裂纹扩展行为的跨尺度分析方法%MULTISCALING ANALYSIS APPROACH OF FATIGUE CRACK GROWTH BEHAVIOR

    Institute of Scientific and Technical Information of China (English)

    唐雪松; 赵小鹏

    2012-01-01

    By taking the dual-scale strain energy density factor as controlling quantity,a multiscaling fatigue crack growth model is developed in this work.Hence,the whole fatigue failure process can be depicted in a consistent way by applying the proposed model.It no longer needs dividing a fatigue process into two different stages of fatigue crack initiation and propagation described by different approaches as usual.Then,the experimental S-N curves for different cyclic stress ratios are exactly re-produced by the proposed model.When the effects of material micro-structure are taken into account,the discrete fatigue test data can be re-produced.The results indicate that the size of initial micro-defects as well as the different evolution modes of material micro-structure have a pronounced influence on the fatigue life of specimens.The microscopic effect is a main reason of the scatter of fatigue test data.%该文以跨尺度应变能密度因子作为裂纹扩展的控制参量,建立了跨尺度疲劳裂纹扩展模型。疲劳破坏全过程可用该模型进行统一描述,而不必划分成疲劳裂纹形成与扩展两个不同阶段,采用不同的理论分别进行分析。以LY12铝合金板为例,采用上述模型,精确拟合出不同循环特征下的S-N试验曲线。当考虑材料微结构的影响时,疲劳试验数据的发散性也可拟合出来。研究表明:材料初始缺陷及微结构在疲劳过程中的演化特性,对于构件的疲劳寿命有显著影响,是疲劳试验数据发散的主要原因。

  15. Altered resting brain connectivity in persistent cancer related fatigue

    Directory of Open Access Journals (Sweden)

    Johnson P. Hampson

    2015-01-01

    Full Text Available There is an estimated 3 million women in the US living as breast cancer survivors and persistent cancer related fatigue (PCRF disrupts the lives of an estimated 30% of these women. PCRF is associated with decreased quality of life, decreased sleep quality, impaired cognition and depression. The mechanisms of cancer related fatigue are not well understood; however, preliminary findings indicate dysfunctional activity in the brain as a potential factor. Here we investigate the relationship between PCRF on intrinsic resting state connectivity in this population. Twenty-three age matched breast cancer survivors (15 fatigued and 8 non-fatigued who completed all cancer-related treatments at least 12 weeks prior to the study, were recruited to undergo functional connectivity magnetic resonance imaging (fcMRI. Intrinsic resting state networks were examined with both seed based and independent component analysis methods. Comparisons of brain connectivity patterns between groups as well as correlations with self-reported fatigue symptoms were performed. Fatigued patients displayed greater left inferior parietal lobule to superior frontal gyrus connectivity as compared to non-fatigued patients (P < 0.05 FDR corrected. This enhanced connectivity was associated with increased physical fatigue (P = 0.04, r = 0.52 and poor sleep quality (P = 0.04, r = 0.52 in the fatigued group. In contrast greater connectivity in the non-fatigued group was found between the right precuneus to the periaqueductal gray as well as the left IPL to subgenual cortex (P < 0.05 FDR corrected. Mental fatigue scores were associated with greater default mode network (DMN connectivity to the superior frontal gyrus (P = 0.05 FDR corrected among fatigued subjects (r = 0.82 and less connectivity in the non-fatigued group (r = −0.88. These findings indicate that there is enhanced intrinsic DMN connectivity to the frontal gyrus in breast cancer survivors with persistent

  16. Effect of age condition on fatigue properties of 2E12 aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    YAN Liang; DU Feng-shan; DAI Sheng-long; YANG Shou-jie

    2010-01-01

    The fatigue behaviors of 2E12 aluminum alloy in T3 and T6 conditions at room temperature in air were investigated.The microstructures and fatigue fracture surfaces of the alloy were examined by transmission electron microscopy(TEM)and scanning electron microscopy(SEM).The results show that the alloy exhibits higher fatigue crack propagation(FCP)resistance in T3condition than in T6 condition,the fatigue life is increased by 54% and the fatigue crack growth rate(FCGR)decreases significantly.The fatigue fractures of the alloy in T3 and T6 conditions are transgranular.But in T3 condition,secondary cracks occur and fatigue striations are not clear.In T6 condition,ductile fatigue striations are observed.The effect of aging conditions on fatigue behaviors is explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.

  17. 合金材料超高周疲劳行为的基本特征和影响因素%ESSENTIAL CHARACTERISTICS AND INFLUENTIAL FACTORS FOR VERY-HIGH-CYCLE FATIGUE BEHAVIOR OF METALLIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    洪友士; 赵爱国; 钱桂安

    2009-01-01

    合金材料在超高周疲劳下具有与低周和高周疲劳不同的裂纹萌生和扩展行为以及不同的S-N曲线特征.材料的强度、循环加载的频率、所处的环境等都显著影响超高周疲劳的特性.本文综述了合金材料超高周疲劳行为的基本特征和影响因素的研究进展.%The research on very-high-cycle fatigue(VHCF)of metallic materials has become a new horizon in the field of metal research since 1980s.The behaviors of crack initiation and propagation,and the characteristics of S-N curve for metallic materials in the VHCF regrime all differ from those in the loW cycle and high cycle fatigue regimes.For VHCF,the cyclic stress is below the level of conventional fatigue 1imit and the crack initiation tends to shift from surface to interior.The defects of material,including inclusions,grain-boundary,phase interface and other miero-inhomogeneities may become interior crack initiation site.The S-N curve containing VHCF regime may present"duplex"or "step-wise"shape.The behaviors of VHCF for metallic materials are substantially affected by the strength of material,loading frequency,loading environment,etc.This paper attempts to review the research progress of essential characteristics and influential factors for VHCF behavior of metallic materials.In addition,the aspects for further research on VHCF of metallic materials are proposed,which are the process and mechanism of fatigue crack initiation and early growth,the effects of loading frequencv and the environment on VHCF property,and development of quantitative model for VHCF.

  18. Tests for fatigue behavior of welded CHS-SHS-concrete filled T-joints%圆管-方管混凝土T型节点疲劳性能试验研究

    Institute of Scientific and Technical Information of China (English)

    童乐为; 杨德磊; Zhao X L

    2013-01-01

    Stress concentration factors(SCF) and fatigue life are two main aspects of studying fatigue behavior of tubular joints based on hot spot stress method. 8 welded CHS-SHS concrete filled T-joints were tested under static loading to determine stress concentration factors at hot spot locations and were also tested under cyclic loading to obtain fatigue life data. The results were compared with those for T-joints made of circular hollow section to square hollow section (CHS-SHS) and no concrete filled. The test results indicated that the CHS-SHS concrete filled T-joints exhibit evident improvements in rigidity distribution and have better anti-fatigue performance than the T-joints made of CHS-SHS and no concrete filled do; S-N curves of hollow section tubular T-joints in the relevant codes are not suitable for fatigue performance analysis of CHS-SHS concrete filled T-joints.%基于热点应力法的管节点疲劳性能研究中,热点应力集中系数和疲劳寿命是描述焊接管结构节点疲劳性能的两个主要因素.对8个支管的圆管主管内填充C50等级混凝土方管节点试件(CT1~CT8)进行热点应力试验以确定其热点应力集中系数(SCF),在此基础上进行疲劳试验以确定其疲劳寿命(N3),将试验结果与具有相同几何尺寸和受力条件的圆管-方管节点试验结果及相关规范进行比较分析.研究表明,支管受轴向荷载下,圆管-方管混凝土节点与对应空钢管节点而言,节点区刚度分布明显改善,前者SCF最大值均小于后者SCF最大值,具有更好的抗疲劳性能;规范中关于空钢管节点疲劳性能的S-N曲线不适用圆管-方管混凝土T型节点的疲劳性能分析.

  19. Fatigue Damage in Wood

    DEFF Research Database (Denmark)

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben;

    1996-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Fatigue failure is found to depend both on the total time under load and on the number of cycles.Recent accelerated fatigue research on wood is reviewed, and a discrepancy between...... failure explanation under fatigue and static load conditions is observed. In the present study small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four frequencies ranging from 0.01 Hz...... to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation between stiffness reduction...

  20. Experimental characterization of fatigue crack tip processes

    Science.gov (United States)

    Lankford, J.; Leverant, G. R.

    1985-01-01

    Many analytical models have been proposed to describe the physical processes attendant to a fatigue crack tip, as well as the rate at which fatigue cracks grow. By applying advanced experimental methods (such as electron channeling, stereoimaging, and in-situ cyclic loading in an SEM) to a broad range of structural materials, it has been shown that it is possible to critically assess the physical assumptions incorporated into the models. Refinements in existing models and the development of new ones have resulted. New insights into materials' behavior are providing guidelines for improving the fatigue resistance of structural alloys. In the near future, even more advanced experimental methods, such as high temperature SEM stages and small angle neutron scattering, will be available to study creep/fatigue interactions in metals and ceramics.

  1. Fatigue of stainless steel in hydrogen

    Science.gov (United States)

    Schuster, G.; Altstetter, C.

    1983-10-01

    The fatigue crack growth rates of two austenitic stainless steel alloys, AISI 301 and 302, were compared in air, argon, and hydrogen environments at atmospheric pressure and room temperature. Under the stresses at the crack tip the austenite in type 301 steel transformed martensitically to a’ to a greater extent than in type 302 steel. The steels were also tested in the cold worked condition under hydrogen or argon. Hydrogen was found to have a deleterious effect on both steels, but the effect was stronger in the unstable than in the stable alloy. Cold work decreased fatigue crack growth rates in argon and hydrogen, but the decrease was less marked in hydrogen than in argon. Metallographic, fractographic, and microhardness surveys in the vicinity of the fatigue crack were used to try to understand the reasons for the observed fatigue behavior.

  2. Low-cycle fatigue of surgical cements

    Directory of Open Access Journals (Sweden)

    A. Balin

    2007-01-01

    Full Text Available Purpose: In case when surgical cement is used to fix endoprostheses of joints the fatigue character of mechanicalinterraction in the cement seems to be a significant importance. The paper suggests to adapt the research methodof low cycle fatigue for modelling the loads on surgical cements in an artificial hip joint. Surgical cements havealso been modified in order to improve their functional properties.Design/methodology/approach: Low cycle fatigue tests were conducted on samples made from Palamedcement without an addition and on samples modified with glassy carbon and titanium. The tests were conductedon a servohydraulic fatigue testing machine, MTS-810, with displacement control.Findings: Fatigue tests proved viscoelastic character of all the tested materials. During the fatigue tests, thephenomenon of stress cyclic relaxation was observed.Research limitations/implications: Modelling the loadings of cement in endoprostheses of joints with the lowcycle fatigue method takes into account all high value stresses, while cement is being used for endoprosthesesfor many years in the conditions of random stress and deformation courses. Therefore the obtained stress anddeformation values are bigger than those which would have been obtained in real conditions in the same time.Practical implications: The low cycle fatigue tests carried out showed how important is the factor of timefor the behavior of surgical cement in the conditions of changeable loadings. This fact is essential to assessits usability for endoprosthesoplasty of joints, specially of a hip joint. Post deformation return which is acharacteristic feature for material viscoelasticity enables its regeneration conditioning expected durability ofendoprosthesis of joints.Originality/value: Low cycle fatigue testing method for modelling of loads on surgical cement in artificial hipjoint enables to carry out the tests in a shorter period of time.

  3. Multiaxial fatigue low cycle fatigue testing

    Science.gov (United States)

    Zamrik, S. Y.

    1985-01-01

    Multiaxial testing methods are reviewed. Advantages and disadvantages of each type test is discussed. Significant multiaxial data available in the literature is analyzed. The yield theories are compared for multiaxial fatigue analysis.

  4. Superior Hiking Trail

    Data.gov (United States)

    Minnesota Department of Natural Resources — Superior Hiking Trail main trail, spurs, and camp spurs for completed trail throughout Cook, Lake, St. Louis and Carlton counties. These data were collected with...

  5. Bathymetry of Lake Superior

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bathymetry of Lake Superior has been compiled as a component of a NOAA project to rescue Great Lakes lake floor geological and geophysical data and make it more...

  6. Superior Hiking Trail Facilities

    Data.gov (United States)

    Minnesota Department of Natural Resources — Superior Hiking Trail main trail, spurs, and camp spurs for completed trail throughout Cook, Lake, St. Louis and Carlton counties. These data were collected with...

  7. The red-eared slider turtle carapace under fatigue loading: The effect of rib-suture arrangement.

    Science.gov (United States)

    Achrai, Ben; Daniel Wagner, H

    2015-08-01

    Biological structures consisting of strong boney elements interconnected by compliant but tough collagenous sutures are abundantly found in skulls and shells of, among others, armadillos, alligators, turtles and more. In the turtle shell, a unique arrangement of alternating rigid (rib) and flexible (suture) elements gives rise to superior mechanical performance when subjected to low and high strain-rate loadings. However, the resistance to repeated load cycling - fatigue - of the turtle shell has yet to be examined. Such repeated loading could approximately simulate the consecutive high-stress bending loads exerted during (a predator) biting or clawing. In the present study flexural high-stress cyclic loads were applied to rib and suture specimens, taken from the top dorsal part of the red-eared slider turtle shell, termed carapace. Subsequently, to obtain a more complete and integrated fatigue behavior of the carapace, specimens containing a complex alternating rib-suture-rib-suture-rib configuration were tested as well. Although the sutures were found to be the least resistant to repeated loads, a synergistic effect was observed for the complex specimens, displaying improved fatigue durability compared to the individual (suture or even rib) constituents. This study may assist in the design of future high-stress fatigue-resistant materials incorporating complex assemblies of rigid and flexible elements. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Causes and consequences of fatigue in rheumatoid arthritis.

    Science.gov (United States)

    Katz, Patricia

    2017-05-01

    To review current information on the causes, treatments, and consequences of fatigue in rheumatoid arthritis. Disease activity (inflammation, pain, joint symptoms) is associated with greater fatigue. However, disease activity per se accounts for only a small portion of fatigue, and rheumatoid arthritis medications that reduce disease activity have small effects on fatigue. Instead, factors outside the direct effects of rheumatoid arthritis, such as obesity, physical inactivity, sleep disturbance, and depression, explain the majority of variation in fatigue. Some of these factors may be indirect effects of disease (e.g. pain can lead to sleep disturbance). Rheumatoid arthritis has significant effects on the quality of life of individuals with rheumatoid arthritis. The most effective approaches to reducing rheumatoid arthritis fatigue appear to be behavioral, such as increasing physical activity, or cognitive, such as cognitive behavioral interventions. Fatigue in rheumatoid arthritis appears to be largely because of factors outside the direct effects of the disease, such as behavioral and psychological factors. In spite of the tremendous impact of fatigue on patient health and quality of life, effective treatments remain elusive, but existing data show that behavioral and cognitive approaches may be most effective.

  9. 正交异性钢桥面板U肋对接焊缝疲劳损伤度分析∗%STUDY OF THE FATIGUE DAMAGE BEHAVIOR OF U-RIB BUTT WELDS OF ORTHOTROPIC STEEL BRIDGE DECK

    Institute of Scientific and Technical Information of China (English)

    王益逊; 吉伯海; 姚悦; 傅中秋; 朱伟

    2016-01-01

    The measuring points were set on the U⁃rib butt welds of fast lane and slow lane in a quarter⁃span of Jiangyin Yangtze River Bridge to measure the one⁃day strain process curves. The curves were filterred by MATLAB software to obtain the real strain process curves of steel box girder under the vehicle loading. The daily damage degree distribution rules of fast and slow lane were analyzed based on the rain flow method and Miner fatigue damage cumulative rule. The daily damage distribution model of U⁃rib butt welds was put forward and the fatigue life of U⁃rib butt welds was evaluated. The analysis result showed that the time when the damage peak of both kinds of lanes occurred was basically the same, yet the peak value differed a lot from each other. The peak value of the slow lane was 4. 4 times than that of the fast lane. The fitting value of fatigue life based on daily damage distribution model coincided well with that of the measured, which could be applied to practical engineerings. The design life of the bridge was superior to and 3. 7 times of the fatigue life of the U⁃rib butt in the slow lane, meaning that the fatigue life of the U⁃rib butt in the slow lane was far from demand, thus special attention should be paid to it.%分别在江阴长江大桥1/4跨截面快车道、慢车道U肋对接焊缝处布设测点,测得该桥一天的应变历程曲线。基于雨流计数法以及Miner疲劳损伤累计准则,分析快、慢车道日损伤度分布规律,并提出了该桥U肋对接焊缝部位的日损伤分布模型,最后对U肋对接焊缝处的疲劳寿命进行评估。分析结果表明,快、慢车道出现损伤峰值的时间基本一致,但各峰值大小差异性较大,慢车道损伤峰值约为快车道损伤峰值的4�4倍;根据日损伤度分布模型得出的疲劳寿命拟合值与实测值吻合良好,可以应用于实际工程;大桥设计寿命约为慢车道U肋对接焊缝实测寿命的3�7

  10. Reducing Uncertainty in Fatigue Life Limits of Turbine Engine Alloys

    Science.gov (United States)

    2014-03-01

    this behavior in turbine engine alloys , we have developed a physically- based approach for describing fatigue var- iability, and this approach has been...of competing mechanisms in the fatigue life variability of a nearly fully-lamellar c-TiAl based alloy . Acta Mater 2005;53:1293–304. [50] Buchanan DJ...Burns JT, Larsen JM, Gangloff RP. Driving forces for localized corrosion -to- fatigue crack transition in Al–Zn– Mg –Cu. Fatigue Fract Eng Mater Struct

  11. Participant attributions for global change ratings in unexplained chronic fatigue and chronic fatigue syndrome.

    Science.gov (United States)

    Friedberg, Fred; Coronel, Janna; Seva, Viktoria; Adamowicz, Jenna L; Napoli, Anthony

    2016-05-01

    The purpose of this mixed methods study was to identify participants' attributions for their global impression of change ratings in a behavioral intervention for unexplained chronic fatigue and chronic fatigue syndrome. At 3-month follow-up, participants (N = 67) were asked "Why do you think you are (improved, unchanged, worse)?" Improved patients pointed to specific behavioral changes, unchanged patients referred to a lack of change in lifestyle, and worsened patients invoked stress and/or specific life events. Identifying patient perceptions of behaviors associated with patient global impression of change-rated improvement and non-improvement may assist in developing more effective management strategies in clinical care.

  12. Compassion fatigue in nurses.

    Science.gov (United States)

    Yoder, Elizabeth A

    2010-11-01

    Compassion fatigue, trigger situations, and coping strategies were investigated in hospital and home care nurses. The Professional Quality of Life Scale measured compassion fatigue, compassion satisfaction, and burnout. Narrative questions elicited trigger situations and coping strategies. Compassion fatigue scores were significantly different between nurses who worked 8- or 12-hour shifts. Fifteen percent of the participants had scores indicating risk of the compassion fatigue. There were significant differences in compassion satisfaction, depending on the unit worked and time as a nurse. The most common category of trigger situations was caring for the patient. Work-related and personal coping strategies were identified. Copyright © 2010 Elsevier Inc. All rights reserved.

  13. The role of physical activity and physical fitness in postcancer fatigue: a randomized controlled trial

    NARCIS (Netherlands)

    Prinsen, H.; Bleijenberg, G.; Heijmen, L.; Zwarts, M.J.; Leer, J.W.H.; Heerschap, A.; Hopman, M.T.E.; Laarhoven, H.W.M. van

    2013-01-01

    PURPOSE: Patients suffering from postcancer fatigue have both an inferior physical activity and physical fitness compared to non-fatigued cancer survivors. The aims of this study were (1) to examine the effect of cognitive behavior therapy, an effective treatment for postcancer fatigue, on physical

  14. FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE

    Directory of Open Access Journals (Sweden)

    Lukáš Bubenko

    2010-10-01

    Full Text Available Austempered ductile iron (ADI has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence of stress intensity factor amplitude to the character of fatigue crack propagation through the ADI microstructure is described.

  15. Bending Fatigue of Carburized Steel at Very Long Lives

    Science.gov (United States)

    Nelson, D. V.; Long, Z.

    2016-01-01

    The bending fatigue behavior of two carburized steels is investigated for lives between approximately 105 and 108 cycles. Cracks are observed to start at sub-surface inclusions and develop features on fracture surfaces resembling "fish eyes" in appearance. This type of sub-surface cracking tends to govern fatigue strength at long lives. Previous studies of "fish eye" fatigue in carburized steel have been relatively few and have mainly considered failures originating at depths beneath a carburized case, where compressive residual stresses are minimal and hardness values approach those in the core. This study provides fatigue data for cracks originating within cases at various depths where compressive residual stresses are substantial and hardness is much higher than in the core. Fatigue strength is predicted by a simple model, accounting for the influence of residual stresses and hardness values at the different depths at which cracks started. Predictions of fatigue strength are compared with data generated in this study.

  16. Analysis of Common Fatigue Details in Steel Truss Structures

    Institute of Scientific and Technical Information of China (English)

    张玉玲; 潘际炎; 潘际銮

    2004-01-01

    Generally, the number of fatigue cycles, the range of the repeated stresses, and the type of the structural details are the key factors affecting fatigue in large-scale welded structures. Seven types of structure details were tested using a 2000-kN hydraulic-pressure-servo fatigue machine to imitate fatigue behavior in modern steel-truss-structures fabricated using thicker welded steel plates and integral joint technology. The details included longitudinal edge welds, welded attachment affecting detail, integral joint, and weld repairs on plate edges. The fatigue damage locations show that the stress (normal or shear), the shape, and the location of the weld start and end points are three major factors reducing the fatigue strength. The test results can be used for similar large structures.

  17. Myth vs. Fact: Adrenal Fatigue

    Science.gov (United States)

    ... unlikely to cover the costs. What is the theory behind adrenal fatigue? Supporters of adrenal fatigue believe ... by producing hormones like cortisol. According to the theory of adrenal fatigue, when people are faced with ...

  18. Chronic Fatigue Syndrome (CFS): Symptoms

    Science.gov (United States)

    ... CDC.gov . Chronic Fatigue Syndrome (CFS) Share Compartir Symptoms On this Page Primary Symptoms Other Symptoms What's ... a doctor distinguish CFS from other illnesses. Primary Symptoms As the name chronic fatigue syndrome suggests , fatigue ...

  19. 搅拌摩擦对接焊6061铝合金的高周疲劳行为%High-cycle fatigue behavior of friction stir butt welded 6061 aluminium alloy

    Institute of Scientific and Technical Information of China (English)

    Hrishikesh DAS; Debayan CHAKRABORTY; Tapan KUMAR PAL

    2014-01-01

    对6061铝合金进行搅拌摩擦对接焊,其焊接工艺参数为:旋转速度600、800、1000、1200 r/min,前进速度80、100 mm/min,探针插入深度1.85 mm。基于搅拌摩擦焊参数计算得到的能量输入结果表明,在输入能量为196~405 kJ的情况下,接头在297~354 kJ的输入能量范围内有最大的抗拉强度。在不同的应力比(R=0.5,0.3,0.1,-0.3,-0.5)下,将高强度、低强度2种焊接头进行疲劳测试。结果表明,对于这2种焊接头,显微组织特征明显影响其疲劳性能,比如搅拌区、热力影响区(TMAZ)和热影响区。从接头的显微组织、裂纹扩展路径和断裂表面观察等方面对其疲劳强度进行讨论。%Friction stir welding (FSW) of 6061 aluminium alloy butt joint was carried out at each rotation speed of 600, 800, 1000, 1200 r/min for two different travel speeds, 80 and 100 mm/min, at a constant probe depth of 1.85 mm. The calculated energy input based on the FSW parameters studied shows that the ultimate tensile strength (UTS) of the butt joint is obtained within a certain range of energy input of 297 kJ to 354 kJ out of total range of energy input studied from 196 kJ to 405 kJ. The fatigue behaviors of high-strength and low-strength joints performed at different stress ratios, i.e., 0.5, 0.3, 0.1, -0.3, -0.5, indicate that the fatigue behaviors of both the welds are sensitive to the microstructural features, such as stir zone (SZ), thermo mechanically affected zone (TMAZ) and heat affected zone (HAZ). The observed fatigue strengths were discussed in terms of the microstructure, crack path behavior and fracture surface.

  20. Fatigue behavior of friction stir spot welded AZ31 Mg alloy sheet joints%AZ31镁合金板材搅拌摩擦点焊连接件的疲劳行为

    Institute of Scientific and Technical Information of China (English)

    罗天骄; 史宝良; 段启强; 付俊伟; 杨院生

    2013-01-01

      利用拉压疲劳实验研究 AZ31板材搅拌摩擦点焊连接件的疲劳行为。结果表明:AZ31镁合金板材搅拌摩擦点焊连接件的疲劳失效均发生在搅拌区,疲劳裂纹均起源于搅拌区外侧边缘,位于上下板之间。当循环加载等于1 kN 时,疲劳裂纹沿着热影响区和热机械区界面且垂直载荷的方向扩展;而当循环载荷等于3 kN时,疲劳裂纹则沿着搅拌区直径方向扩展,并最终发生剪切断裂。另外,断口横截面显微分析显示,在AZ31板间搅拌区外侧存在一个“舌状区”,“舌状区”的方向是沿搅拌区向外,疲劳裂纹均起源于“舌状区”。%The fatigue behavior of friction stir spot welded (FSSW) AZ31 magnesium alloy sheet joints was investigated by tension−compression of fatigue test. The results suggest that all the fatigue failures occur at the stir zone of the FSSW AZ31 sheet joints, and all cracks initiate at the stir zone outer edge between the upper and lower sheet. When the cycle force equals 1 kN, the crack propagates along the interface of heat-affected zone and thermo-mechanical zone, simultaneously across the direction of force;while the cycle force equals 3 kN, the crack propagates along the diameter of stir zone and shear failure occurs finally. Moreover, the transverse microsections indicate that there is a tongue-like region at the outer edge of stir zone between the two AZ31 sheets, and the direction of tongue-like region is toward outside of the stirred zone and all fatigue cracks initiate at the tongue-like region.

  1. PERSISTENT LEFT SUPERIOR VENACAVA

    Directory of Open Access Journals (Sweden)

    Devinder Singh

    2014-05-01

    Full Text Available A Persistent Left Superior Venacava (PLSVC is the most common variation of the thoracic venous system and rare congenital vascular anomaly and is prevalent in 0.3% of the population. It may be associated with other cardiovascular abnormalities including atrial septal defect, bicuspid aortic valve, coarctation of aorta, coronary sinus ostial atresia, and cor triatriatum. Incidental rotation of a dilated coronary sinus on echocardiography should raise the suspicion of PLSVC. The diagnosis should be confirmed by saline contrast echocardiography. Condition is usually asymptomatic. Here we present a rare case of persistent left superior vena cava presented in OPD with dyspnoea & palpitations.

  2. CAD/CAM machining Vs pre-sintering in-lab fabrication techniques of Y-TZP ceramic specimens: Effects on their mechanical fatigue behavior.

    Science.gov (United States)

    Zucuni, C P; Guilardi, L F; Fraga, S; May, L G; Pereira, G K R; Valandro, L F

    2017-03-18

    This study evaluated the effects of different pre-sintering fabrication processing techniques of Y-TZP ceramic (CAD/CAM Vs. in-lab), considering surface characteristics and mechanical performance outcomes. Pre-sintered discs of Y-TZP ceramic (IPS e.max ZirCAD, Ivoclar Vivadent) were produced using different pre-sintering fabrication processing techniques: Machined- milling with a CAD/CAM system; Polished- fabrication using a cutting device followed by polishing (600 and 1200 SiC papers); Xfine- fabrication using a cutting machine followed by grinding with extra-fine diamond bur (grit size 30 μm); Fine- fabrication using a cutting machine followed by grinding with fine diamond bur (grit size 46 μm); SiC- fabrication using a cutting machine followed by grinding with 220 SiC paper. Afterwards, the discs were sintered and submitted to roughness (n=35), surface topography (n=2), phase transformation (n=2), biaxial flexural strength (n=20), and biaxial flexural fatigue strength (fatigue limit) (n=15) analyses. No monoclinic-phase content was observed in all processing techniques. It can be observed that obtaining a surface with similar characteristics to CAD/CAM milling is essential for the observation of similar mechanical performance. On this sense, grinding with fine diamond bur before sintering (Fine group) was the best mimic protocol in comparison to the CAD/CAM milling.

  3. Fatigue Management in Spaceflight Operations

    Science.gov (United States)

    Whitmire, Alexandra

    2011-01-01

    Sleep loss and fatigue remain an issue for crewmembers working on the International Space Station, and the ground crews who support them. Schedule shifts on the ISS are required for conducting mission operations. These shifts lead to tasks being performed during the biological night, and sleep scheduled during the biological day, for flight crews and the ground teams who support them. Other stressors have been recognized as hindering sleep in space; these include workload, thinking about upcoming tasks, environmental factors, and inadequate day/night cues. It is unknown if and how other factors such as microgravity, carbon dioxide levels, or increased radiation, may also play a part. Efforts are underway to standardize and provide care for crewmembers, ground controllers and other support personnel. Through collaborations between research and operations, evidenced-based clinical practice guidelines are being developed to equip flight surgeons with the tools and processes needed for treating circadian desynchrony (and subsequent sleep loss) caused by jet lag and shift work. The proper implementation of countermeasures such as schedules, lighting protocols, and cognitive behavioral education can hasten phase shifting, enhance sleep and optimize performance. This panel will focus on Fatigue Management in Spaceflight Operations. Speakers will present on research-based recommendations and technologies aimed at mitigating sleep loss, circadian desynchronization and fatigue on-orbit. Gaps in current mitigations and future recommendations will also be discussed.

  4. 一种超高碳钢的滚动接触疲劳研究%ROLLING CONTACT FATIGUE BEHAVIOR OF AN ULTRAHIGH CARBON STEEL

    Institute of Scientific and Technical Information of China (English)

    刘宏基; 孙俊杰; 江涛; 郭生武; 柳永宁; 林鑫

    2014-01-01

    研究了一种C含量为1.29%(质量分数)的超高碳钢在最大Hertzian应力4400 MPa,良好润滑条件下的滚动接触疲劳行为,同时测试了传统GCr15和SKF3高碳铬轴承钢的滚动接触疲劳寿命以作为对比.结果表明,相同条件下,超高碳钢的额定寿命(L10寿命)分别是GCr15钢和SKF3钢的2.14和1.81倍.超高碳钢的原奥氏体平均晶粒尺寸为6.91μm,仅约为GCr15和SKF3钢的一半.同时,淬回火态超高碳钢的硬度为64.5 HRC,高于GCr15和SKF3钢.%With the development of modern industrial equipment and the requirement in energy conservation and emission reduction,the traditional high carbon and high chromium steel which is widely used as bearing material cannot meet these demands.Therefore,it is of paramount importance to exploit novel materials used as bearings with long life.In recent years,some new techniques have been used to improve the bearing life,such as physical vapor deposition (PVD),chemical vapor deposition (CVD) and plasma immersion implantation and so on.All these techniques are attempting to increase the surface hardness of the bearing.Though the bearing life has been extended to some extent,the application range of these techniques is limited by the price factor and the dimensions of components.Ultrahigh-carbon steels (UHCSs) have been studied for many years,and they possess outstanding mechanical properties and wear resistance.Therefore,it is interesting to explore the probability whether UHCSs can be used in the beating application.It is well known that if bearings are well assembled,lubricated and loaded,rolling contact fatigue (RCF) is the main failure form.Accordingly,the evaluation of the resistance to RCF is of paramount importance for bearing materials.The RCF properties of UHCSs have never been studied in the past decades.Therefore,in this work,the RCF behavior of a UHCS with 1.29%C (mass fraction) was investigated in well lubricated conditions,using a flat washer-type RCF

  5. Examining fatigue in COPD

    DEFF Research Database (Denmark)

    Al-Shair, Khaled; Muellerova, Hana; Yorke, Janelle

    2012-01-01

    ABSTRACT: INTRODUCTION: Fatigue is a disruptive symptom that inhibits normal functional performance of COPD patients in daily activities. The availability of a short, simple, reliable and valid scale would improve assessment of the characteristics and influence of fatigue in COPD. METHODS......: At baseline, 2107 COPD patients from the ECLIPSE cohort completed the Functional Assessment of Chronic Illness Therapy Fatigue (FACIT-F) scale. We used well-structured classic method, the principal components analysis (PCA) and Rasch analysis for structurally examining the 13-item FACIT-F. RESULTS: Four items...... were less able to capture fatigue characteristics in COPD and were deleted. PCA was applied to the remaining 9 items of the modified FACIT-F and resulted in three interpretable dimensions: i) general (5 items); ii) functional ability (2 items); and iii) psychosocial fatigue (2 items). The modified...

  6. Compressive Fatigue in Wood

    DEFF Research Database (Denmark)

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben;

    1999-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four...... frequencies ranging from 0.01 Hz to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation...... is observed between stiffness reduction and accumulated creep. A failure model based on the total work during the fatigue life is rejected, and a modified work model based on elastic, viscous and non-recovered viscoelastic work is experimentally supported, and an explanation at a microstructural level...

  7. Characterization of the fatigue behavior of the medial collateral ligament utilizing traditional and novel mechanical variables for the assessment of damage accumulation.

    Science.gov (United States)

    Zec, Michelle L; Thistlethwaite, Paul; Frank, Cyril B; Shrive, Nigel G

    2010-01-01

    Ligaments are regularly subjected to repetitive loading in vivo. Typically, mechanical studies focus on repetitive loading protocols of short duration, while those characterizing damage accumulation over a longer duration (i.e., fatigue studies) are lacking. The aims of this study were as follows: (a) to demonstrate that damage does accumulate in ligament tissue subjected to repetitive loading and (b) to evaluate existing and new methods for characterizing fatigue damage accumulation. It was hypothesized that ligaments would accumulate damage with repetitive loading as evidenced by failure at stresses well below ultimate tensile strength, creep curve discontinuities, and by reductions in stiffness during loading. Eight normal medial collateral ligaments from female New Zealand white rabbits were cycled in tension, between 0 MPa and 28 MPa, to failure or until 259,200 cycles, whichever came first. Medial collateral ligaments that did not fail were subsequently loaded to failure. Displacement rates (dl(max)/dt) as well as primary, secondary, and tertiary creeps were monitored as indices of damage accumulation and impending mechanical failure. Additionally, the relative utilities of tangent, secant, and chord stiffness parameters were critically evaluated. Finally, new uses for the second derivative of force-displacement data were explored. Three out of eight ligaments failed during testing, demonstrating that ligaments can fail in fatigue under moderate tensile stress in vitro. The evaluation of displacement rates (dl(max)/dt), as well as primary through tertiary creep patterns, were not well suited to predicting failure in normal ligaments until rupture was all but imminent. Tangent stiffness, which was calculated from a mathematically defined start of the "linear region," was surprisingly constant throughout testing. Secant stiffness dropped in a predictable fashion, providing a global indicator of tissue stiffness, but did not provide any insight into fiber

  8. Fatigue crack propagation behavior in the field of residual stress distribution. 7th Report. Study of fatigue crack propagation behavior based upon RPG load; Zanryu oryokuba ni okeru hiro kiretsu denpa kyodo. 7. RPG kijun ni yoru hiro kiretsu denpa kyodo no kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Toyosada, M.; Niwa, T. [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering

    1995-12-01

    In the previous report, load causing tensional plastic region or in other words the load limit above RPG load was an effective load limit for fatigue crack propagation and corresponding to this, the relation between the stress expansion coefficient limit {delta}K{sub RP} and fatigue crack propagation rate including the periphery of lower limit region showed linear relation in logarithm graph. In this report, many informations were achieved from the fatigue crack propagation experiment under same load condition using center notched specimens for the three cases such as tension residual stress and compression residual stress are applied to the near edges of the specimen, and for the case where residual stress do not exist in order to study whether the stress expansion coefficient limit {delta}K{sub RP} corresponding to load range above RPG load can be a parameter of fatigue crack propagation rate or not even in case of residual stress field and further, whether the simulation of RPG load can be materialize even in case of residual stress field or not. 6 refs., 9 figs., 2 tabs.

  9. 热处理对Al-Si-Cu-Mg铸造铝合金低周疲劳行为的影响%Influence of Heat Treatment on Low-Cycle Fatigue Behavior of Al-Si-Cu-Mg Alloy

    Institute of Scientific and Technical Information of China (English)

    李锋; 陈巧; 车欣; 陈立佳

    2012-01-01

    为了确定固溶处理及固溶+时效处理对金属型铸造A1-Si-Cu-Mg铝合金低周疲劳行为的影响,在不同外加总应变幅下进行应变控制的室温低周疲劳试验.结果表明:金属型铸造Al-Si-Cu-Mg铝合金可表现为循环应变硬化、循环应变软化和循环稳定;固溶处理及固溶+时效处理可以有效地提高金属型铸造Al-Si-Cu-Mg铝合金的疲劳寿命,且固溶处理对疲劳寿命提高的幅度更大;铸态及固溶态Al-Si-Cu-Mg铝合金的弹性应变幅、塑性应变幅与疲劳断裂时的载荷反向周次之间分别呈直线关系,固溶+时效态Al-Si-Cu-Mg铝合金的弹性应变幅与疲劳断裂时的载荷反向周次之间呈直线关系,但其塑性应变幅与疲劳断裂时的载荷反向周次之间呈双线性关系;不同处理状态的铸造Al-Si-Cu-Mg铝合金的循环应力幅与塑性应变幅之间呈线性关系.%In order to determine the influence of solid-solution and solid-solution plus aging treatments on low-cycle fatigue behavior of permanent-mold cast Al-Si-Cu-Mg alloy, the strain controlled low-cycle fatigue tests were performed at room temperature and different total strain amplitudes. The experimental results show that the permanent-mold cast Al-Si-Cu-Mg alloy exhibits the cyclic strain hardening, softening and stability. The solid-solution and solid-solution plus aging treatments can effectively enhance the fatigue lives of the permanent-mold cast Al-Si-Cu-Mg alloy, and the solid-solution treatment has more significant in enhancing the fatigue lives of the alloy. A single-slope linear relationship between plastic and elastic strain amplitudes as well as reversals to failure is observed for both as-cast and solid-solution treated Al-Si-Cu-Mg alloys. For the permanent-mold cast Al-Si-Cu-Mg alloy subjected to solid-solution plus aging treatment, the relationship between elastic strain amplitude and reversals to failure also shows linear behavior, but a bilinear

  10. Self-regulatory fatigue in chronic multisymptom illnesses: scale development, fatigue, and self-control.

    Science.gov (United States)

    Nes, Lise Solberg; Ehlers, Shawna L; Whipple, Mary O; Vincent, Ann

    2013-01-01

    Self-regulatory capacity involves ability to regulate thoughts, emotions, and behavior. Chronic multisymptom illnesses such as fibromyalgia and chronic fatigue syndrome are accompanied by numerous challenges, and have recently been associated with self-regulatory fatigue (SRF). Chronic multisymptom illnesses are also frequently associated with physical fatigue, and through development of a scale measuring SRF, the current study aimed to examine how SRF can be distinguished from physical fatigue. The study also sought to distinguish SRF from self-control. Two self-regulation researchers developed 30 items related to self-regulatory capacity. These items were distributed to patients (n = 296) diagnosed with chronic multisymptom illness together with validated measures of physical fatigue and self-control. A principal factor analysis was employed to examine factor structures, identify inter-item relationships, and aid in scale development. The final proposed scale consisted of 18 items measuring self-regulatory capacity (SRF-18) with cognitive, emotional, and behavioral SRF components. Internal consistency and reliability was acceptable (Cronbach's á = 0.81). The final scale was moderately correlated with self-control (r = -0.48) and highly correlated with physical fatigue (r = 0.75), although more so with emotional (r = 0.72) and mental (r = 0.65) than physical (r = 0.46) fatigue components. The current study suggests a new scale for measurement of SRF in chronic multisymptom illness. Although cross-validation studies are necessary, such a scale may contribute to a better understanding of the concept of self-regulation and the role of SRF in chronic illness. Although related to physical fatigue and self-control, the results point to SRF as a distinct construct.

  11. Memory for Fatigue in Chronic Fatigue Syndrome: Relationships to Fatigue Variability, Catastrophizing, and Negative Affect

    Science.gov (United States)

    Sohl, Stephanie J.; Friedberg, Fred

    2008-01-01

    Fatigue in chronic fatigue syndrome (CFS) is usually assessed with retrospective measures rather than real-time momentary symptom assessments. In this study, the authors hypothesized that in participants with CFS, discrepancies between recalled and momentary fatigue would be related to catastrophizing, anxiety, and depression and to variability of momentary fatigue. They also expected that catastrophizing, anxiety, and depression would be associated with momentary fatigue. The authors asked 53 adults with CFS to carry electronic diaries for 3 weeks and record their experiences of momentary fatigue. The authors assessed participants' fatigue recall with weekly ratings and administered questionnaires for catastrophizing, depression, and anxiety. Recall discrepancy was significantly related to the variability of momentary fatigue. In addition, catastrophizing, depression, and momentary fatigue were all significantly related to recall discrepancy. Catastrophizing, depression, anxiety, and momentary negative affect were all significantly associated with momentary fatigue. The findings suggest that momentary fatigue in patients with CFS is related to modifiable psychological factors. PMID:18400687

  12. Fatigue Management (La Gestion de la Fatigue)

    Science.gov (United States)

    1991-12-01

    Management Pre’face Etant donne la tenidance de plus en plus marque ~e vets le maintien en service des aironefs au-delak des dates lintites...transport aircraft designed prototype sade its first flight one year about 20 years ago; from the fatigue point later. The results of the flight testing

  13. Atomistic Mechanisms of Fatigue in Nanocrystalline Metals

    Science.gov (United States)

    Farkas, D.; Willemann, M.; Hyde, B.

    2005-04-01

    We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2.

  14. Thermomechanical Multiaxial Fatigue Testing Capability Developed

    Science.gov (United States)

    1996-01-01

    Structural components in aeronautical gas turbine engines typically experience multiaxial states of stress under nonisothermal conditions. To estimate the durability of the various components in the engine, one must characterize the cyclic deformation and fatigue behavior of the materials used under thermal and complex mechanical loading conditions. To this end, a testing protocol and associated test control software were developed at the NASA Lewis Research Center for thermomechanical axial-torsional fatigue tests. These tests are to be performed on thin-walled, tubular specimens fabricated from the cobalt-based superalloy Haynes 188. The software is written in C and runs on an MS-DOS based microcomputer.

  15. Fatigue evaluation algorithms: Review

    Energy Technology Data Exchange (ETDEWEB)

    Passipoularidis, V.A.; Broendsted, P.

    2009-11-15

    A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. FADAS (Fatigue Damage Simulator) 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 multiaxial 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. (author)

  16. Experiences of Fatigue at Sea

    DEFF Research Database (Denmark)

    Zhao, Zhiwei; Jepsen, Jørgen Riis; Chen, Zhonglong

    2016-01-01

    Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T-test t...

  17. Prolonged unexplained fatigue in paediatrics

    NARCIS (Netherlands)

    Bakker, R.J.

    2010-01-01

    Prolonged Unexplained Fatigue in Paediatrics. Fatigue, as the result of mental or physical exertion, will disappear after rest, drinks and food. Fatigue as a symptom of illness will recover with the recovering of the illness. But when fatigue is ongoing for a long time, and not the result of exertio

  18. Experiences of Fatigue at Sea

    DEFF Research Database (Denmark)

    Zhao, Zhiwei; Jepsen, Jørgen Riis; Chen, Zhonglong;

    2016-01-01

    Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T...

  19. Dramatic increase in fatigue life in hierarchical graphene composites.

    Science.gov (United States)

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

    2010-10-01

    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.

  20. Air Superiority Fighter Characteristics.

    Science.gov (United States)

    1998-06-05

    many a dispute could have been deflated into a single paragraph if the disputants had just dared to define their terms.7 Aristotle ...meaningful. This section will expand on some key ideology concepts. The phrase "air superiority fighter" may bring to mind visions of fighter... biographies are useful in garnering airpower advocate theories as well as identifying key characteristics. Air campaign results, starting with World

  1. Metabolic Factors in Fatigue

    Institute of Scientific and Technical Information of China (English)

    Mark Hargreaves

    2006-01-01

    Increased non-oxidative and oxidative ATP production via metabolic pathways in skeletal muscle is essential for the maintenance of force and power production during exercise. However, substrate depletion and accumulation of metabolic byproducts are potential causes of fatigue. Reduced PCr availability can limit power production during sprint exercise, whereas carbohydrate depletion is a major limitation to endurance performance. During sprint exercise increased Pi and H+ may contribute to fatigue, and during prolonged strenuous exercise, the accumulation of NH3, reactive oxygen species, and heat can limit performance. Appropriate training programs and nutritional interventions are potential strategies to enhance fatigue resistance and exercise performance.

  2. Fatigue 󈨛. Volume 2,

    Science.gov (United States)

    1987-06-01

    fatigue cracks grown in a nominally elastic field. EXPERIMENTAL DETAILS A low alloy steel (QIN) with a composition closely similar to HY80 , i.e. 2.5...Prediction of Steel Cords - A. PRAKASH, 645 G.A. COSTELLO, R.M. SHEMENSKI AND D.K. KIM Effect of Hold Time on Fatigue of Lead Rich 655 PbSn Solder...S. VAYNMAN, M.E. FINE AND D.A. JEANNOTTE On Cleavage in Fatigue for Rail Steels - 667 ZHU DONG, CAI QIGONG and YAO HENG Influence of Cleavage on

  3. Environmental heat stress enhances mental fatigue during sustained attention task performing: evidence from an ASL perfusion study.

    Science.gov (United States)

    Qian, Shaowen; Li, Min; Li, Guoying; Liu, Kai; Li, Bo; Jiang, Qingjun; Li, Li; Yang, Zhen; Sun, Gang

    2015-03-01

    This study was to investigate the potential enhancing effect of heat stress on mental fatigue progression during sustained attention task using arterial spin labeling (ASL) imaging. Twenty participants underwent two thermal exposures in an environmental chamber: normothermic (NT) condition (25°C, 1h) and hyperthermic (HT) condition (50°C, 1h). After thermal exposure, they performed a twenty-minute psychomotor vigilance test (PVT) in the scanner. Behavioral analysis revealed progressively increasing subjective fatigue ratings and reaction time as PVT progressed. Moreover, heat stress caused worse performance. Perfusion imaging analyses showed significant resting-state cerebral blood flow (CBF) alterations after heat exposure. Specifically, increased CBF mainly gathered in thalamic-brainstem area while decreased CBF predominantly located in fronto-parietal areas, anterior cingulate cortex, posterior cingulate cortex, and medial frontal cortex. More importantly, diverse CBF distributions and trend of changes between both conditions were observed as the fatigue level progressed during subsequent PVT task. Specifically, higher CBF and enhanced rising trend were presented in superior parietal lobe, precuneus, posterior cingulate cortex and anterior cingulate cortex, while lower CBF or inhibited rising trend was found in dorsolateral frontal cortex, medial frontal cortex, inferior parietal lobe and thalamic-brainstem areas. Furthermore, the decrease of post-heat resting-state CBF in fronto-parietal cortex was correlated with subsequent slower reaction time, suggesting prior disturbed resting-state CBF might be indicator of performance potential and fatigue level in following task. These findings may provide proof for such a view: heat stress has a potential fatigue-enhancing effect when individual is performing highly cognition-demanding attention task.

  4. Fatigue test of carbon epoxy composite high pressure hydrogen storage vessel under hydrogen environment

    Institute of Scientific and Technical Information of China (English)

    Chuan-xiang ZHENG; Liang WANG; Rong LI; Zong-xin WEI; Wei-wei ZHOU

    2013-01-01

    A significant temperature raise within hydrogen vehicle cylinder during the fast filling process will be observed,while the strength and fatigue life of the cylinder will dramatically decrease at high temperature.In order to evaluate the strength and fatigue of composite hydrogen storage vessel,a 70-MPa fatigue test system using hydrogen medium was set up.Experimental study on the fatigue of composite hydrogen storage vessels under real hydrogen environment was performed.The experimental results show that the ultimate strength and fatigue life both decreased obviously compared with the values under hydraulic fatigue test.Furthermore,fatigue property,failure behavior,and safe hydrogen charging/discharging working mode of onboard hydrogen storage vessels were obtained through the fatigue tests.

  5. The use of methylphenidate to relieve fatigue.

    Science.gov (United States)

    Rojí, Rocío; Centeno, Carlos

    2017-09-06

    To review recent evidence on the efficacy and safety of methylphenidate as a symptomatic treatment of patients with cancer-related fatigue (CRF). Five clinical trials published since 2011 were identified. Two of these concluded that methylphenidate is more efficacious than placebo in providing relief from CRF, but the remaining three showed no difference in favour of methylphenidate. The studies were heterogeneous as per the dosage, scales used for evaluating fatigue and the target group studied. None of the studies detected serious reactions, and only mild and infrequent side-effects of methylphenidate were reported. Three new metanalyses show the slightly superior effect of methylphenidate compared to placebo in CRF. Overall, literature supports the existence of moderate benefit of methylphenidate in CRF, backed up by weak evidence. Future studies should aim at better identifying the profile of patients who would benefit most from this pharmacological intervention.

  6. AI-Si-Cu-Mg(-Er)铸造铝合金的低周疲劳行为%Low-Cycle Fatigue Behavior of Cast AI-Si-Cu-Mg(-Er) Aluminum Alloy

    Institute of Scientific and Technical Information of China (English)

    车欣; 徐志军; 陈立佳; 徐海健; 李锋

    2011-01-01

    对金属型铸造Al-Si-Cu-Mg和Al-Si-Cu-Mg-Er铝合金进行了疲劳试验,并研究了其室温下的低周疲劳行为.试验结果表明:金属型铸造Al-Si-Cu-Mg和Al-Si-Cu-Mg-Er铝合金表现为循环应变硬化和循环稳定,主要取决于外加总应变的高低;稀土元素Er的加入可提高金属型铸造Al-Si-Cu-Mg合金的循环变形抗力和疲劳寿命;金属型铸造Al-Si-Cu-Mg合金的塑性应变、弹性应变与断裂时的载荷反向次数之间呈直线关系,Al-Si-Cu-Mg-Er合金的弹性应变与疲劳断裂时的载荷反向次数之间也呈直线关系,但其塑性应变与疲劳断裂时的载荷反向次数之间则呈双线性关系.%Through the strain-controlled fatigue experiments, the low-cycle fatigue behavior of permanent-mold cast Al-Si-Cu-Mg and Al-Si-Cu-Mg-Er alloys at room temperature was investigated.The experimental results show that the Al-Si-Cu-Mg and Al-Si-Cu-Mg-Er alloys exhibit the cyclic strain hardening and cyclic stability, mainly depending on the imposed total strain amplitude. For the permanent-mold cast Al-Si-Cu-Mg alloy, the addition of Er can effectively enhance both cyclic deformation resistance and fatigue life of the alloys. A single-slope linear relation between plastic strain amplitude, elastic strain amplitude and reversals to failure is observed for permanent-mold cast Al-Si-Cu-Mg alloy. However, a two-slope linear relation between plastic strain amplitude and reversals to failure is noted for the Al-Si-Cu-Mg-Er alloy, although the corresponding relation between elastic strain amplitude and reversals to failure is linear.

  7. AZ31B镁合金焊接接头的疲劳裂纹扩展行为%Fatigue Crack Propagation Behavior of as-Extruded AZ31B Mg Alloy Welded Joint

    Institute of Scientific and Technical Information of China (English)

    张红霞; 裴飞飞; 闫志峰; 王文先; 梁培阳; 李娟; 卫英慧

    2012-01-01

    The fatigue crack propagation behavior of as-extruded AZ31B magnesium alloy welded joint and heat affected zone have been studied.Compact tensions [C(T)] of welded joint [L-T(W)] and heat affected zone(welded joint is parallel [T-L(H)]and vertical [L-T(H)] to the extruded direction) were researched.Results indicate that the crack propagation direction is parallel to the extrusion direction for L-T(W); fatigue crack propagation rate is a rapid-slow process.T-L(H) is parallel to the notch direction and L-T(H) can be divided into two states (i.e.,parallel to or angularly deflected towards the notch direction);crack propagation rate initially goes through a rapid course before it slows down.The fracture modes of crack tip remain a mixed-mode of transgranular and intergranular fractures.The fatigue fracture consists of quasi-cleavage and is a brittle fracture.%对AZ31B镁合金焊接接头和热影响区的疲劳裂纹扩展行为进行研究,分析了焊接接头[L-T(W)]和热影响区的紧凑拉伸试验[C(T)],其中热影响区的C(T)试验包括焊缝平行于挤压方向[T-L(H)]和垂直于挤压方向[L-T(H)]两种.结果表明:对于L-T(W)试样,裂纹沿挤压方向扩展,裂纹扩展经历先快后慢的扩展过程;T-L(H)试样裂纹平行于缺口方向扩展,L-T(H)试样裂纹为平行于缺口方向和与缺口成一定角度两种扩展方向,裂纹扩展经历先慢后快的扩展过程.裂纹尖端扩展为穿晶和沿晶的混合模式,疲劳断口为准解理特征的脆性断口.

  8. A Constitutive Relationship between Fatigue Limit and Microstructure in Nanostructured Bainitic Steels.

    Science.gov (United States)

    Mueller, Inga; Rementeria, Rosalia; Caballero, Francisca G; Kuntz, Matthias; Sourmail, Thomas; Kerscher, Eberhard

    2016-10-14

    The recently developed nanobainitic steels show high strength as well as high ductility. Although this combination seems to be promising for fatigue design, fatigue properties of nanostructured bainitic steels are often surprisingly low. To improve the fatigue behavior, an understanding of the correlation between the nanobainitic microstructure and the fatigue limit is fundamental. Therefore, our hypothesis to predict the fatigue limit was that the main function of the microstructure is not necessarily totally avoiding the initiation of a fatigue crack, but the microstructure has to increase the ability to decelerate or to stop a growing fatigue crack. Thus, the key to understanding the fatigue behavior of nanostructured bainite is to understand the role of the microstructural features that could act as barriers for growing fatigue cracks. To prove this hypothesis, we carried out fatigue tests, crack growth experiments, and correlated these results to the size of microstructural features gained from microstructural analysis by light optical microscope and EBSD-measurements. Finally, we were able to identify microstructural features that influence the fatigue crack growth and the fatigue limit of nanostructured bainitic steels.

  9. A Constitutive Relationship between Fatigue Limit and Microstructure in Nanostructured Bainitic Steels

    Directory of Open Access Journals (Sweden)

    Inga Mueller

    2016-10-01

    Full Text Available The recently developed nanobainitic steels show high strength as well as high ductility. Although this combination seems to be promising for fatigue design, fatigue properties of nanostructured bainitic steels are often surprisingly low. To improve the fatigue behavior, an understanding of the correlation between the nanobainitic microstructure and the fatigue limit is fundamental. Therefore, our hypothesis to predict the fatigue limit was that the main function of the microstructure is not necessarily totally avoiding the initiation of a fatigue crack, but the microstructure has to increase the ability to decelerate or to stop a growing fatigue crack. Thus, the key to understanding the fatigue behavior of nanostructured bainite is to understand the role of the microstructural features that could act as barriers for growing fatigue cracks. To prove this hypothesis, we carried out fatigue tests, crack growth experiments, and correlated these results to the size of microstructural features gained from microstructural analysis by light optical microscope and EBSD-measurements. Finally, we were able to identify microstructural features that influence the fatigue crack growth and the fatigue limit of nanostructured bainitic steels.

  10. Numerical simulation of thermo-mechanical fatigue properties for particulate reinforced composites

    Institute of Scientific and Technical Information of China (English)

    Ran Guo; Huiji Shi; Zhenhan Yao

    2005-01-01

    In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites.The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermomechanical behavior. Some related conclusions are obtained by examples of numerical simulation.

  11. Neurocognitive impairment in childhood chronic fatigue syndrome

    Directory of Open Access Journals (Sweden)

    Kei eMizuno

    2013-04-01

    Full Text Available Neurocognitive impairment is a feature of childhood chronic fatigue syndrome (CCFS. Several studies have demonstrated reduced attention control in CCFS patients in switching and divided attention tasks. In students, the extent of deterioration in task performance depends on the level of fatigue. Poor performance in switching and divided attention is common in both fatigued students and CCFS patients. Additionally, attentional functions show dramatic development from childhood to adolescence, suggesting that abnormal development of switching and divided attention may be induced by chronic fatigue. The brain structures associated with attentional control are situated in the frontal and parietal cortices, which are the last to mature, suggesting that severe fatigue in CCFS patients and students may inhibit normal structural and functional development in these regions. A combination of treatment with cognitive behavioral therapy and antidepressant medication is effective to improve attentional control processing in CCFS patients. Studies identifying the features of neurocognitive impairment in CCFS have improved our current understanding of the neurophysiological mechanisms of CCFS.

  12. Pilot's visual attention allocation modeling under fatigue.

    Science.gov (United States)

    Wu, Xu; Wanyan, Xiaoru; Zhuang, Damin

    2015-01-01

    Human factors involved with visual attention mechanism and fatigue are critical causes of modern aviation accidents. To investigate the connection between attention and flight fatigue, a mathematical model of pilot's visual attention allocation was established based on information processing channels. Multi-task condition and current psychophysical state were taken into account as well. Sixteen participants were recruited to perform a long-term dual-task in a Boeing 737-800 flight simulator. The primary task was an envelope flight task and the secondary was an unusual attitude (UA) recovery task. Reaction time of the secondary task was recorded as a behavior performance index, while heart rate and respiration rate were measured as physiological indices as well as fixation distribution as attention allocation index. The experiment results showed a significant affect of experiment time that indicated the occurrence and influence of fatigue. Eye movement tracking also revealed good agreement with the predictable model and hence verified its effectiveness. Moreover, applicability of the model was validated under flight fatigue and multiple tasks condition. The current study provided a quantitative connection between pilot's visual attention allocation and flight fatigue, which was verified in the ergonomics experiment.

  13. Hyperthermia and fatigue

    DEFF Research Database (Denmark)

    Nybo, Lars

    2008-01-01

    of the cardiovascular function, which eventually reduces arterial oxygen delivery to the exercising muscles. Accordingly, aerobic energy turnover is impaired and anaerobic metabolism provokes peripheral fatigue. In contrast, metabolic disturbances of muscle homeostasis are less important during prolonged exercise......The present review addresses mechanisms of importance for hyperthermia-induced fatigue during short intense activities and prolonged exercise in the heat. Inferior performance during physical activities with intensities that elicit maximal oxygen uptake is to a large extent related to perturbation...... of the dopaminergic system, but may primarily relate to inhibitory signals from the hypothalamus arising secondary to an increase in brain temperature. Fatigue is an integrated phenomenon, and psychological factors, including the anticipation of fatigue, should not be neglected and the interaction between central...

  14. Fatigue Evaluation Algorithms: Review

    DEFF Research Database (Denmark)

    Passipoularidis, Vaggelis; Brøndsted, Povl

    A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. FADAS (Fatigue Damage Simulator) 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 multiaxial load time...... 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...

  15. Fatigue in soccer

    DEFF Research Database (Denmark)

    Mohr, Magni; Krustrup, Peter; Bangsbo, Jens

    2005-01-01

    This review describes when fatigue may develop during soccer games and the potential physiological mechanisms that cause fatigue in soccer. According to time?-?motion analyses and performance measures during match-play, fatigue or reduced performance seems to occur at three different stages......, acidity or the breakdown of creatine phosphate. Instead, it may be related to disturbances in muscle ion homeostasis and an impaired excitation of the sarcolemma. Soccer players' ability to perform maximally is inhibited in the initial phase of the second half, which may be due to lower muscle...... concentrations in a considerable number of individual muscle fibres. In a hot and humid environment, dehydration and a reduced cerebral function may also contribute to the deterioration in performance. In conclusion, fatigue or impaired performance in soccer occurs during various phases in a game, and different...

  16. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    evaluating ciack initiation time and crack propagation, prgram I was used for performing the major fatigue test with the aircraft structure. In...advantage to begin with the end of the fracture, this is especially so in the case of the quantitative evaluation of striations. The overload fracture...Select the Measuring Line for Quantitative Evaluation Actually, the fatigue fracture should be inspected completely from the point of origin to the

  17. The Recognition Of Fatigue

    DEFF Research Database (Denmark)

    Elsass, Peter; Jensen, Bodil; Mørup, Rikke;

    2007-01-01

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

  18. Driver Fatigue Features Extraction

    Directory of Open Access Journals (Sweden)

    Gengtian Niu

    2014-01-01

    Full Text Available Driver fatigue is the main cause of traffic accidents. How to extract the effective features of fatigue is important for recognition accuracy and traffic safety. To solve the problem, this paper proposes a new method of driver fatigue features extraction based on the facial image sequence. In this method, first, each facial image in the sequence is divided into nonoverlapping blocks of the same size, and Gabor wavelets are employed to extract multiscale and multiorientation features. Then the mean value and standard deviation of each block’s features are calculated, respectively. Considering the facial performance of human fatigue is a dynamic process that developed over time, each block’s features are analyzed in the sequence. Finally, Adaboost algorithm is applied to select the most discriminating fatigue features. The proposed method was tested on a self-built database which includes a wide range of human subjects of different genders, poses, and illuminations in real-life fatigue conditions. Experimental results show the effectiveness of the proposed method.

  19. Fatigue Crack Growth Threshold Testing of Metallic Rotorcraft Materials

    Science.gov (United States)

    Newman, John A.; James, Mark A.; Johnson, William M.; Le, Dy D.

    2008-01-01

    Results are presented for a program to determine the near-threshold fatigue crack growth behavior appropriate for metallic rotorcraft alloys. Four alloys, all commonly used in the manufacture of rotorcraft, were selected for study: Aluminum alloy 7050, 4340 steel, AZ91E Magnesium, and Titanium alloy Ti-6Al-4V (beta-STOA). The Federal Aviation Administration (FAA) sponsored this research to advance efforts to incorporate damage tolerance design and analysis as requirements for rotorcraft certification. Rotorcraft components are subjected to high cycle fatigue and are typically subjected to higher stresses and more stress cycles per flight hour than fixed-wing aircraft components. Fatigue lives of rotorcraft components are generally spent initiating small fatigue cracks that propagate slowly under near-threshold cracktip loading conditions. For these components, the fatigue life is very sensitive to the near-threshold characteristics of the material.

  20. Contabilidad Financiera Superior

    OpenAIRE

    Ipiñazar Petralanda, Izaskun

    2013-01-01

    Duración (en horas): De 31 a 40 horas. Destinatario: Estudiante y Docente A través de este material se presentan las pautas necesarias para implementar un aprendizaje basado en problemas en la asignatura de Contabilidad Financiera Superior dentro de los temas “Constitución de S.A. y S.R.L.” (Tema 2), “Ampliaciones de Capital” (Tema 3) y “Reducciones de Capital” (Tema 4). En primer lugar se presentan las guías generales de la asignatura, y a continuación, las diferentes activida...

  1. Contabilidad Financiera Superior

    OpenAIRE

    Ipiñazar Petralanda, Izaskun

    2013-01-01

    Duración (en horas): De 31 a 40 horas. Destinatario: Estudiante y Docente A través de este material se presentan las pautas necesarias para implementar un aprendizaje basado en problemas en la asignatura de Contabilidad Financiera Superior dentro de los temas “Constitución de S.A. y S.R.L.” (Tema 2), “Ampliaciones de Capital” (Tema 3) y “Reducciones de Capital” (Tema 4). En primer lugar se presentan las guías generales de la asignatura, y a continuación, las diferentes activida...

  2. Experimental Study on High Cycle Fatigue Behavior andγ-P-S-N Curves of Bridge Steel Q345qD%Q345qD桥梁钢高周疲劳性能及γ-P-S-N曲线试验研究

    Institute of Scientific and Technical Information of China (English)

    贾单锋; 廖小伟; 崔佳

    2016-01-01

    针对桥梁钢Q345qD的力学性能及高周疲劳特性,分别使用直径10,mm的圆棒试件和沙漏型试件进行了轴向拉伸试验及轴向疲劳试验,得到 Q345qD 完整的材性数据及应力-寿命曲线(S-N 曲线)。考虑到材料疲劳寿命离散性较大,为了便于工程应用,采用单侧容限统计方法,研究在给定置信度下各应力水平对应的 Q34qD 的安全疲劳寿命,得出了同时考虑置信度和存活率的设计疲劳曲线。研究结果表明桥梁钢 Q345qD 在常温下具有较好的疲劳性能,随应力水平的降低疲劳寿命明显增大,疲劳寿命曲线迅速趋于水平,疲劳极限在Smax=273~278,MPa之间。%The mechanical properties and high cycle fatigue behavior of bridge steel Q345qD were studied.A number of axial tensile tests and axial fatigue tests were conducted using 10,mm-diameter round bar specimens and hourglass specimens respectively.The accurate data of material properties and stress-life curve(S-N curve)were ob-tained.Taking into account the large discreteness of material fatigue life,in order to facilitate engineering applica-tions,unilateral tolerance statistical methods were adopted to study the Q345qD safety fatigue life at a given confi-dence level for each stress level.The safe life fatigue curves with confidence and survival rate were also obtained.The results show that the bridge steel Q345qD has good fatigue properties at room temperature.The fatigue life increases significantly with the decrease of stress level and the fatigue curve tends to reach the horizontal level quickly.The fatigue limit lies within the range ofSmax=273—278,MPa.

  3. Mg-12Gd-3Y-0.5Zr镁合金的不同疲劳行为%Different Fatigue Behaviors of Mg-12Gd-3Y-0.5Zr Magnesium Alloy

    Institute of Scientific and Technical Information of China (English)

    杨晓明; 杨帆; 尹树明; 王渠东; 吴世丁; 张哲峰; 李守新

    2011-01-01

    Room temperature low cycle fatigue, very high cycle fatigue, high temperature isothermal fatigue and thermo-mechanical fatigue properties of the as-rolled Mg-12Gd-3Y-0.5Zr magnesium alloy were investigated.The fatigue failure mechanism was analyzed.The results show that for room temperature low cycle fatigue and very high cycle fatigue, the failure was caused by the fatigue cracks resulted from the inclusions or large-sized secondary phases.The cracks initiated from the surface or sub-surface for low cycle fatigue, however, for very high cycle fatigue the internal cracking was the initiation.Both high temperaturei sothermal fatigue crack and thermomechanical fatigue crack originated from the surface.The interaction of cyclic slip and oxide inclusions was the main fatigue mechanism.The alloy had excellent tensile strength and fatigue strength from room temperature to 200 ℃.The opposed phase thermo-mechanical fatigue lifetime was longer than the in-phase one thermo-mechanical fatigue lifetime.%对轧制态Mg-12Gd-3Y-0.5Zr镁合金的室温低周、超高周疲劳,高温等温疲劳以及热机械疲劳性能进行了研究,并对其疲劳失效机制进行了分析.结果表明:对室温低周疲劳、超高周疲劳来说,其失效机制主要是夹杂或大的第二相引起的疲劳开裂;对于低周疲劳,裂纹萌生于表面或亚表面,而对于超高周疲劳,裂纹起源于内部;该合金的高温等温疲劳与热机械疲劳断裂裂纹都萌生于表面,其疲劳机制为循环滑移和氧化物夹杂共同作用;该合金在室温到200℃有良好的抗拉强度与疲劳强度;反相位热机械疲劳寿命比同相位的高.

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

    Directory of Open Access Journals (Sweden)

    F. Morel

    2015-07-01

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

  5. Statistics of superior records

    Science.gov (United States)

    Ben-Naim, E.; Krapivsky, P. L.

    2013-08-01

    We study statistics of records in a sequence of random variables. These identical and independently distributed variables are drawn from the parent distribution ρ. The running record equals the maximum of all elements in the sequence up to a given point. We define a superior sequence as one where all running records are above the average record expected for the parent distribution ρ. We find that the fraction of superior sequences SN decays algebraically with sequence length N, SN˜N-β in the limit N→∞. Interestingly, the decay exponent β is nontrivial, being the root of an integral equation. For example, when ρ is a uniform distribution with compact support, we find β=0.450265. In general, the tail of the parent distribution governs the exponent β. We also consider the dual problem of inferior sequences, where all records are below average, and find that the fraction of inferior sequences IN decays algebraically, albeit with a different decay exponent, IN˜N-α. We use the above statistical measures to analyze earthquake data.

  6. Frenillo labial superior doble

    Directory of Open Access Journals (Sweden)

    Carlos Albornoz López del Castillo

    Full Text Available El frenillo labial superior doble no sindrómico es una anomalía del desarrollo que no hemos encontrado reportada en la revisión bibliográfica realizada. Se presenta una niña de 11 años de edad que fue remitida al servicio de Cirugía Maxilofacial del Hospital "Eduardo Agramonte Piña", de Camagüey, por presentar un frenillo labial superior doble de baja inserción. Se describen los síntomas clínicos asociados a esta anomalía y el tratamiento quirúrgico utilizado para su solución: una frenectomía y plastia sobre la banda muscular frénica anormal que provocaba exceso de tejido en la mucosa labial. Consideramos muy interesante la descripción de este caso, por no haber encontrado reporte similar en la literatura revisada.

  7. A study of spectrum fatigue crack propagation in two aluminum alloys. 2: Influence of microstructures

    Science.gov (United States)

    Telesman, J.; Antolovich, S. D.

    1985-01-01

    The important metallurgical factors that influence both constant amplitude and spectrum crack growth behavior in aluminum alloys were investigated. The effect of microstructural features such as grain size, inclusions, and dispersoids was evaluated. It was shown that a lower stress intensities, the I/M 7050 alloy showed better fatigue crack propagation (FCP) resistance than P/M 7091 alloy for both constant amplitude and spectrum testing. It was suggested that the most important microstructural variable accounting for superior FCP resistance of 7050 alloy is its large grain size. It was further postulated that the inhomogenous planar slip and large grain size of 7050 limit dislocation interactions and thus increase slip reversibility which improves FCP performance. The hypothesis was supported by establishing that the cyclic strain hardening exponent for the 7091 alloy is higher than that of 7050.

  8. Total strain version of strainrange partitioning for thermomechanical fatigue at low strains

    Science.gov (United States)

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

    1987-01-01

    A new method is proposed for characterizing and predicting the thermal fatigue behavior of materials. The method is based on three innovations in characterizing high temperature material behavior: (1) the bithermal concept of fatigue testing; (2) advanced, nonlinear, cyclic constitutive models; and (3) the total strain version of traditional strainrange partitioning.

  9. a Study on the Fretting Fatigue Life of Zircaloy Alloys

    Science.gov (United States)

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

    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.

  10. Fatigue Properties of Plain Concrete Under Triaxial Compressive Cyclic Loading

    Institute of Scientific and Technical Information of China (English)

    曹伟; 宋玉普; 刘海成

    2004-01-01

    Experiments were made on plain concrete subjected to triaxial static loading and constant-amplitude compressive fatigue loading with a constant lateral pressure in two directions. The initial confining pressure was O, 0. 1fc, 0.25fc andO. 4fc, respectively, for the static test, and 0. 1fc and 0.25fc for the fatigue test. Based on the triaxial compressive constitutive behavior of concrete, the inflexion of confining pressure evolution was chosen to be the fatigue damage criterion during the test. The rule of evolution of longitudinal maximum and minimum strains, longitudinal cyclic modulus and damage were recorded and analyzed. According to the Fardis-Chen criterion model and the concept of equivalent fatigue life and equivalent stress level, a unified S-N curve for multi-axial compressive fatigue loading was proposed. Thus, the fatigue strength factors for different fatigue loading cases can be obtained. The present investigation provides information for the fatigue design of concrete structures.

  11. Suppression of Fatigue Crack Propagation of Duralumin by Cavitation Peening

    Directory of Open Access Journals (Sweden)

    Hitoshi Soyama

    2015-08-01

    Full Text Available It was demonstrated in the present paper that cavitation peening which is one of the mechanical surface modification technique can suppress fatigue crack propagation in duralumin. The impacts produced when cavitation bubble collapses can be utilised for the mechanical surface modification technique in the same way as laser peening and shot peening, which is called “cavitation peening”. Cavitation peening employing a cavitating jet in water was used to treat the specimen made of duralumin Japanese Industrial Standards JIS A2017-T3. After introducing a notch, fatigue test was conducted by a load-controlled plate bending fatigue tester, which has been originally developed. The fatigue crack propagation behavior was evaluated and the relationship between the fatigue crack propagation rate versus stress intensity factor range was obtained. From the results, the fatigue crack propagation rate was drastically reduced by cavitation peening and the fatigue life of duralumin plate was extended 4.2 times by cavitation peening. In addition, the fatigue crack propagation can be suppressed by 88% in the stable crack propagation stage by cavitation peening.

  12. A review on fatigue life prediction methods for anti-vibration rubber materials

    Directory of Open Access Journals (Sweden)

    Xiaoli WANG

    2016-08-01

    Full Text Available Anti-vibration rubber, because of its superior elasticity, plasticity, waterproof and trapping characteristics, is widely used in the automotive industry, national defense, construction and other fields. The theory and technology of predicting fatigue life is of great significance to improve the durability design and manufacturing of anti-vibration rubber products. According to the characteristics of the anti-vibration rubber products in service, the technical difficulties for analyzing fatigue properties of anti-vibration rubber materials are pointed out. The research progress of the fatigue properties of rubber materials is reviewed from three angles including methods of fatigue crack initiation, fatigue crack propagation and fatigue damage accumulation. It is put forward that some nonlinear characteristics of rubber under fatigue loading, including the Mullins effect, permanent deformation and cyclic stress softening, should be considered in the further study of rubber materials. Meanwhile, it is indicated that the fatigue damage accumulation method based on continuum damage mechanics might be more appropriate to solve fatigue damage and life prediction problems for complex rubber materials and structures under fatigue loading.

  13. Creep, fatigue and creep-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels

    Science.gov (United States)

    Kalyanasundaram, Valliappa

    Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated temperature structural components. Creep-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the creep, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (creep, fatigue and C-F) on grade P91 steel at 625°C in a round-robin (RR) program. Along with 7 creep deformation and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal creep deformation and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625°C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of

  14. The effect of osteoporosis treatments on fatigue properties of cortical bone tissue

    Directory of Open Access Journals (Sweden)

    Garry R. Brock

    2015-06-01

    Full Text Available Bisphosphonates are commonly prescribed for treatment of osteoporosis. Long-term use of bisphosphonates has been correlated to atypical femoral fractures (AFFs. AFFs arise from fatigue damage to bone tissue that cannot be repaired due to pharmacologic treatments. Despite fatigue being the primary damage mechanism of AFFs, the effects of osteoporosis treatments on fatigue properties of cortical bone are unknown. To examine if fatigue-life differences occur in bone tissue after different pharmacologic treatments for osteoporosis, we tested bone tissue from the femurs of sheep given a metabolic acidosis diet to induce osteoporosis, followed by treatment with a selective estrogen reception modulator (raloxifene, a bisphosphonate (alendronate or zoledronate, or parathyroid hormone (teriparatide, PTH. Beams of cortical bone tissue were created and tested in four-point bending fatigue to failure. Tissue treated with alendronate had reduced fatigue life and less modulus loss at failure compared with other treatments, while tissue treated with PTH had a prolonged fatigue life. No loss of fatigue life occurred with zoledronate treatment despite its greater binding affinity and potency compared with alendronate. Tissue mineralization measured by microCT did not explain the differences seen in fatigue behavior. Increased fatigue life with PTH suggests that current treatment methods for AFF could have beneficial effects for restoring fatigue life. These results indicate that fatigue life differs with each type of osteoporosis treatment.

  15. Fatigue failure of hydrogen embrittled high strength steels

    Science.gov (United States)

    Kim, Y. G.; Aleszka, J.

    1975-01-01

    Results of an experimental investigation are presented concerning the fracture behavior of cathodically charged, quenched and tempered martensitic steels under cyclic load conditions. Introduction of H2 by cathodic charging reduced fatigue life by as much as 60%. It is proposed that subsurface transverse fatigue cracks nucleate simultaneously at multiple sites, such as at microcracks, voids, or inclusions. Fatigue crack growth then occurs on planes perpendicular to the major applied stress axis in the presence of the critical combination of applied external stress and hydrogen.

  16. Thermal fatigue of beryllium

    Energy Technology Data Exchange (ETDEWEB)

    Deksnis, E.; Ciric, D.; Falter, H. [JET Joint undertaking, Abingdon (United Kingdom)] [and others

    1995-09-01

    Thermal fatigue life of S65c beryllium castellated to a geometry 6 x 6 x (8-10)mm deep has been tested for steady heat fluxes of 3 MW/m{sup 2} to 5 MW/m{sup 2} and under pulsed heat fluxes (10-20 MW/m{sup 2}) for which the time averaged heat flux is 5 MW/m{sup 2}. These tests were carried out in the JET neutral beam test facility A test sequence with peak surface temperatures {le} 600{degrees}C produced no visible fatigue cracks. In the second series of tests, with T{sub max} {le} 750{degrees}C evidence for fatigue appeared after a minimum of 1350 stress cycles. These fatigue data are discussed in view of the observed lack of thermal fatigue in JET plasma operations with beryllium PFC. JET experience with S65b and S65c is reviewed; recent operations with {Phi} = 25 MW/m{sup 2} and sustained melting/resolidification are also presented. The need for a failure criterion for finite element analyses of Be PFC lifetimes is discussed.

  17. Fatigue characteristics and microcosmic mechanism of Al-Si-Mg alloys under multiaxial proportional loadings

    Science.gov (United States)

    Jiang, Xiao-Song; He, Guo-Qiu; Liu, Bing; Zhu, Zheng-Yu; Zhang, Wei-Hua

    2011-08-01

    With the increasing use of Al-Si-Mg alloys in the automotive industry, the fatigue performance of Al-Si-Mg alloy has become a major concern with regard to their reliability. The fatigue characteristics and microcosmic mechanism of an Al-Si-Mg alloy under multiaxial proportional loadings were investigated in this research. As low cycle fatigue life and material strengthening behavior are closely related, the effect of equivalent strain amplitude on the multiaxial fatigue properties was analyzed. Fatigue tests were conducted to determine the influence of equivalent strain amplitude on the multiaxial proportional fatigue properties. The fatigue life exhibits a stable behavior under multiaxial proportional loadings. The dislocation structures of the Al-Si-Mg alloy were observed by transmission electron microscopy (TEM). The dislocation structure evolution of the Al-Si-Mg alloy under multiaxial proportional loadings during low cycle fatigue develops step by step by increasing fatigue cycles. Simultaneously, the dislocation structure changes with the change in equivalent strain amplitude under multiaxial proportional loadings. The experimental evidence indicates that the multiaxial fatigue behavior and life are strongly dependent on the microstructure of the material, which is caused by multiaxial proportional loadings.

  18. Relationship between fatigue life in the creep-fatigue region and stress-strain response

    Science.gov (United States)

    Berkovits, A.; Nadiv, S.

    1988-01-01

    On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the two more pairs of stress strain parameters must be ascertained.

  19. Fatigue life prediction in composites

    CSIR Research Space (South Africa)

    Huston, RJ

    1994-01-01

    Full Text Available as the modulus is measured accurately. Its main disadvantage is that it can be applied only to constant amplitude fatigue loadings. REFERENCES 1. Mandell, J. F., Huang, D. D. & McGarry, F. J., Tensile fatigue performance...

  20. Cyclic deformation, fatigue and fatigue crack propagation in Ni-base alloys

    Science.gov (United States)

    Antolovich, Stephen D.; Lerch, Brad

    1989-01-01

    Ni-base superalloys' cumulative glide behavior, damage accumulation, low-cycle fatigue, and crack propagation characteristics are directly dependent on deformation behavior which is in turn a strong function of microstructural characteristics. Microstructural instabilities and environmental interactions become additional factors at elevated temperatures. An account is presently given of microstructural, chemical, and processing techniques that may be used to obtain the properties that appear most critical or desirable in specific applications.