A transient plasticity study and low cycle fatigue analysis of the Space Station Freedom photovoltaic solar array blanket

NASA Technical Reports Server (NTRS)

Armand, Sasan C.; Liao, Mei-Hwa; Morris, Ronald W.

1990-01-01

The Space Station Freedom photovoltaic solar array blanket assembly is comprised of several layers of materials having dissimilar elastic, thermal, and mechanical properties. The operating temperature of the solar array, which ranges from -75 to +60 C, along with the material incompatibility of the blanket assembly components combine to cause an elastic-plastic stress in the weld points of the assembly. The weld points are secondary structures in nature, merely serving as electrical junctions for gathering the current. The thermal mechanical loading of the blanket assembly operating in low earth orbit continually changes throughout each 90 min orbit, which raises the possibility of fatigue induced failure. A series of structural analyses were performed in an attempt to predict the fatigue life of the solar cell in the Space Station Freedom photovoltaic array blanket. A nonlinear elastic-plastic MSC/NASTRAN analysis followed by a fatigue calculation indicated a fatigue life of 92,000 to 160,000 cycles for the solar cell weld tabs. Additional analyses predict a permanent buckling phenomenon in the copper interconnect after the first loading cycle. This should reduce or eliminate the pulling of the copper interconnect on the joint where it is welded to the silicon solar cell. It is concluded that the actual fatigue life of the solar array blanket assembly should be significantly higher than the calculated 92,000 cycles, and thus the program requirement of 87,500 cycles (orbits) will be met. Another important conclusion that can be drawn from the overall analysis is that, the strain results obtained from the MSC/NASTRAN nonlinear module are accurate to use for low-cycle fatigue analysis, since both thermal cycle testing of solar cells and analysis have shown higher fatigue life than the minimum program requirement of 87,500 cycles.

Irradiation creep-fatigue interaction of type 316L stainless steel

NASA Astrophysics Data System (ADS)

Scholz, R.; Mueller, R.

1996-10-01

Type 316L stainless steel samples in both, 20% cold-worked (cw) and recrystallised (rc) conditions were exposed to strain controlled fatigue cycling in torsion at 400°C during an irradiation with 19 MeV deuterons. The effect of irradiation creep induced stress relaxation on the fatigue life was studied by imposing a hold time at the minimum strain value in the loading cycle. For the cw material at strain ranges of 1.13% and 1.3%, the absolute stress values, τ H, maintained during the hold time decreased with the number of cycles due to the irradiation creep induced stress relaxation. A mean stress was built up. The number of cycles to failure was considerably reduced in comparison to continuous cycling tests under thermal conditions. For the rc material at strain ranges of 1.03% and 1.4%, the values of τ H increased with the number of cycles, despite the hold time imposed, due to irradiation and/or cyclic hardening.

High temperature fatigue behavior of tungsten copper composites

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.; Kim, Yong-Suk; Gabb, Timothy P.

1989-01-01

The high temperature fatigue behavior of a 9 vol percent, tungsten fiber reinforced copper matrix composite was investigated. Load-controlled isothermal fatigue experiments 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 displayed considerable inelasticity under all conditions. Also, strain ratcheting was observed during all the fatigue experiments. For the isothermal fatigue and in-phase TMF tests, the ratcheting was always in a tensile direction, continuing until failure. The ratcheting during the out-of-phase TMF test shifted from a tensile direction to a compressive direction. This behavior was thought to be associated with the observed bulging and the extensive cracking of the out-of-phase specimen. For all cases, the fatigue lives were found to be controlled by damage to the copper matrix. Grain boundary cavitation was the dominant damage mechanism of the matrix. On a stress basis, TMF loading reduced lives substantially, relative to isothermal cycling. In-phase cycling resulted in the shortest lives, and isothermal fatigue at 260 C, the longest.

Notched fatigue of single crystal PWA 1480 at turbine attachment temperatures

NASA Technical Reports Server (NTRS)

Meyer, T. G.; Nissley, D. M.; Swanson, G. A.

1989-01-01

The focus is on the lower temperature, uncoated and notched features of gas turbine blades. Constitutive and fatigue life prediction models applicable to these regions are being developed. Fatigue results are presented which were obtained thus far. Fatigue tests are being conducted on PWA 1480 single crystal material using smooth strain controlled specimens and three different notched specimens. Isothermal fatigue tests were conducted at 1200, 1400, and 1600 F. The bulk of the tests were conducted at 1200 F. The strain controlled tests were conducted at 0.4 percent per second strain rate and the notched tests were cycled at 1.0 cycle per second. A clear orientation dependence is observed in the smooth strain controlled fatigue results. The fatigue lifes of the thin, mild notched specimens agree fairly well with this smooth data when elastic stress range is used as a correlating parameter. Finite element analyses were used to calculate notch stresses. Fatigue testing will continue to further explore the trends observed thus far. Constitutive and life prediction models are being developed.

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

NASA Technical Reports Server (NTRS)

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.

PO2 cycling reduces diaphragm fatigue by attenuating ROS formation.

PubMed

Zuo, Li; Diaz, Philip T; Chien, Michael T; Roberts, William J; Kishek, Juliana; Best, Thomas M; Wagner, Peter D

2014-01-01

Prolonged muscle exposure to low PO2 conditions may cause oxidative stress resulting in severe muscular injuries. We hypothesize that PO2 cycling preconditioning, which involves brief cycles of diaphragmatic muscle exposure to a low oxygen level (40 Torr) followed by a high oxygen level (550 Torr), can reduce intracellular reactive oxygen species (ROS) as well as attenuate muscle fatigue in mouse diaphragm under low PO2. Accordingly, dihydrofluorescein (a fluorescent probe) was used to monitor muscular ROS production in real time with confocal microscopy during a lower PO2 condition. In the control group with no PO2 cycling, intracellular ROS formation did not appear during the first 15 min of the low PO2 period. However, after 20 min of low PO2, ROS levels increased significantly by ∼30% compared to baseline, and this increase continued until the end of the 30 min low PO2 condition. Conversely, muscles treated with PO2 cycling showed a complete absence of enhanced fluorescence emission throughout the entire low PO2 period. Furthermore, PO2 cycling-treated diaphragm exhibited increased fatigue resistance during prolonged low PO2 period compared to control. Thus, our data suggest that PO2 cycling mitigates diaphragm fatigue during prolonged low PO2. Although the exact mechanism for this protection remains to be elucidated, it is likely that through limiting excessive ROS levels, PO2 cycling initiates ROS-related antioxidant defenses.

Design and fabrication of the Mini-Brayton Recuperator (MBR)

NASA Technical Reports Server (NTRS)

Killackey, J. J.; Graves, R.; Mosinskis, G.

1978-01-01

Development of a recuperator for a 2.0 kW closed Brayton space power system is described. The plate-fin heat exchanger is fabricated entirely from Hastelloy X and is designed for 10 years continuous operation at 1000 K (1300 F) with a Xenon-helium working fluid. Special design provisions assure uniform flow distribution, crucial for meeting 0.975 temperature effectiveness. Low-cycle fatigue, resulting from repeated startup and shutdown cycles, was identified as the most critical structural design problem. It is predicted that the unit has a minimum fatigue life of 220 cycles. This is in excess of the BIPS requirement of 100 cycles. Heat transfer performance and thermal cycle testing with air, using a prototype unit, verified that all design objectives can be met.

Influences of Processing and Fatigue Cycling on Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

NASA Astrophysics Data System (ADS)

Gabb, T. P.; Rogers, R. B.; Nesbitt, J. A.; Miller, R. A.; Puleo, B. J.; Johnson, D.; Telesman, J.; Draper, S. L.; Locci, I. E.

2017-11-01

Oxidation and corrosion can attack superalloy disk surfaces exposed to increasing operating temperatures in some turbine engine environments. Any potential protective coatings must also be resistant to harmful fatigue cracking during service. The objective of this study was to investigate how residual stresses evolve in one such coating. Fatigue specimens of a powder metallurgy-processed disk superalloy were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of this processing and fatigue cycling on axial residual stresses and other aspects of the coating were assessed. While shot peening did induce beneficial compressive residual stresses in the coating and substrate, these stresses relaxed in the coating with subsequent heating. Several cast alloys having compositions near the coating were subjected to thermal expansion and tensile stress relaxation tests to help explain this response of residual stresses in the coating. For the coated fatigue specimens, this response contributed to earlier cracking of the coating than for the uncoated surface during long intervals of cycling at 760 °C. Yet, substantial compressive residual stresses still remained in the substrate adjacent to the coating, which were sufficient to suppress fatigue cracking there. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

Comparison of cyclic fatigue and torsional resistance in reciprocating single-file systems and continuous rotary instrumentation systems.

PubMed

da Frota, Matheus F; Espir, Camila G; Berbert, Fábio L C V; Marques, André A F; Sponchiado-Junior, Emílio C; Tanomaru-Filho, Mario; Garcia, Lucas F R; Bonetti-Filho, Idomeo

2014-12-01

As compared with continuous rotary systems, reciprocating motion is believed to increase the fatigue resistance of NiTi instruments. We compared the cyclic fatigue and torsional resistance of reciprocating single-file systems and continuous rotary instrumentation systems in simulated root canals. Eighty instruments from the ProTaper Universal, WaveOne, MTwo, and Reciproc systems (n = 20) were submitted to dynamic bending testing in stainless-steel simulated curved canals. Axial displacement of the simulated canals was performed with half of the instruments (n = 10), with back-and-forth movements in a range of 1.5 mm. Time until fracture was recorded, and the number of cycles until instrument fracture was calculated. Cyclic fatigue resistance was greater for reciprocating systems than for rotary systems (P < 0.05). Instruments from the Reciproc and WaveOne systems significantly differed only when axial displacement occurred (P < 0.05). Instruments of the ProTaper Universal and MTwo systems did not significantly differ (P > 0.05). Cyclic fatigue and torsional resistance were greater for reciprocating systems than for continuous rotary systems, irrespective of axial displacement.

Low cycle fatigue

NASA Technical Reports Server (NTRS)

Solomon, H. D. (Editor); Kaisand, L. R. (Editor); Halford, G. R. (Editor); Leis, B. N. (Editor)

1988-01-01

The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime prediction of a nickel-base ODS alloy, and an integrated approach to creep-fatigue life prediction. Other topics discussed include thermal fatigue testing of coated monocrystalline superalloys, low cycle fatigue of Al-Mg-Si alloys, and the effect of superimposed stresses at high frequency on low cycle fatigue.

Relationship between functional electrical stimulation duty cycle and fatigue in wrist extensor muscles of patients with hemiparesis.

PubMed

Packman-Braun, R

1988-01-01

The purpose of this study was to investigate, in a sample of patients with hemiparesis secondary to cerebrovascular accident, the relationship between the ratio of stimulus on time to off time and muscle fatigue using a commercial electrical stimulation unit. An experimental model was used to test the hypothesis that the smaller the stimulus off time relative to stimulus on time, the greater will be the muscle fatigue over time. The wrist extensor muscles of 18 patients with hemiparesis were stimulated electrically, and isometric force output was recorded continuously using an adapted strain gauge-recorder apparatus. For each testing session, peak on time of the electrical stimulus was set at 5 seconds, and off time was set at 5, 15, or 25 seconds. Six randomly assigned treatment groups participated in three separate treatment sessions in a different order at 48-hour intervals. Treatment sessions were continued either until wrist extensor muscle force output decreased to 50% of its initial value or for a maximum of 30 minutes. Data analysis revealed that significant differences in muscle tension developed among all duty cycles (p less than .01). Duty-cycle ratios of 1:1, 1:3, and 1:5 were shown to be progressively less fatiguing. Within the limits of this investigation, the 1:5 duty-cycle ratio was determined to be the best suited for initial use in programs of prolonged stimulation to the wrist extensor muscles of patients with hemiparesis. The hypothesis was accepted that the smaller the stimulus off time (rest interval) with respect to the stimulus on time, the greater will be the muscle fatigue over time.

Dynamic strain aging behavior of modified 9Cr-1Mo and reduced activation ferritic martensitic steels under low cycle fatigue

NASA Astrophysics Data System (ADS)

Mariappan, K.; Shankar, Vani; Sandhya, R.; Prasad Reddy, G. V.; Mathew, M. D.

2013-04-01

Influence of temperature and strain rate on low cycle fatigue (LCF) behavior of modified 9Cr-1Mo ferritic martensitic steel and 1.4W-0.06Ta reduced activation ferritic martensitic (RAFM) steel in normalized and tempered conditions was studied. Total strain controlled LCF tests between 300 and 873 K on modified 9Cr-1Mo steel and RAFM steel and at various strain rates on modified 9Cr-1Mo steel were performed at total strain amplitude of ±0.6%. Both the steels showed continuous cyclic softening at all temperatures. Whereas manifestations of dynamic strain aging (DSA) were observed in both the steels which decreased fatigue life at intermediate temperatures, at higher temperatures, oxidation played a crucial role in decreasing fatigue life.

Effect of Variable Amplitude Blocks' Ordering on the Functional Fatigue of Superelastic NiTi Wires

NASA Astrophysics Data System (ADS)

Soul, Hugo; Yawny, Alejandro

2017-12-01

Accumulation of superelastic cycles in NiTi uniaxial element generates changes on the stress-strain response. Basically, there is an uneven drop of martensitic transformation stress plateaus and an increase of residual strain. This evolution associated with deterioration of superelastic characteristics is referred to as "functional fatigue" and occurs due to irreversible microstructural changes taking place each time a material domain transforms. Unlike complete cycles, for which straining is continued up to elastic loading of martensite, partial cycles result in a differentiated evolution of those material portions affected by the transformation. It is then expected that the global stress-strain response would reflect the previous cycling history of the specimen. In the present work, the consequences of cycling of NiTi wires using blocks of different strain amplitudes interspersed in different sequences are analyzed. The effect of successive increasing, successive decreasing, and interleaved strain amplitudes on the evolution of the superelastic response is characterized. The feasibility of postulating a functional fatigue criterion similar to the Miner's cumulative damage law used in structural fatigue analysis is discussed. The relation of the observed stress-strain response with the transformational history of the specimen can be rationalized by considering that the stress-induced transformation proceeds via localized propagating fronts.

Thermal-mechanical fatigue of high temperature structural materials

NASA Astrophysics Data System (ADS)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

Fracture morphologies of carbon-black-loaded SBR (styrene-butadiene rubber) subjected to low-cycle, high-stress fatigue. [Styrene-butadiene rubber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldberg, A.; Lesuer, D.R.; Patt, J.

Experimental results, together with an analytical model, related to the loss in tensile strength of styrene-butadiene rubber (SBR) loaded with carbon black (CB) that had been subjected to low-cycle, high-stress fatigue tests were presented in a prior paper. The drop in tensile strength relative to that of a virgin sample was considered to be a measure of damage induced during the fatigue test. The present paper is a continuation of this study dealing with the morphological interpretations of the fractured surfaces, whereby the cyclic-tearing behavior, resulting in the damage, is related to the test and material parameters. It was foundmore » that failure is almost always initiated in the bulk of a sample at a material flaw. The size and definition of a flaw increase with an increase in carbon-black loading. Initiation flaw sites are enveloped by fan-shaped or penny-shaped regions which develop during cycling. The size and morphology of a fatigue-tear region appears to be independent of the fatigue load or the extent of the damage (strength loss). By contrast, either an increase in cycling load or an increase in damage at constant load increases the definition of the fatigue-region morphology for all formulations of carbon-black. On the finest scale, the morphology can be described in terms of tearing of individual groups of rubber strands, collapsing to form a cell-like structure. 18 refs., 13 figs.« less

Strain differences in fatigue and depression after experimental stroke.

PubMed

Kunze, Allison; Zierath, Dannielle; Drogomiretskiy, Olga; Becker, Kyra

2014-10-01

Fatigue and depression are common symptoms after stroke. Animal models of poststroke fatigue (PSF) and poststroke depression (PSD) would facilitate the study of these symptoms. Spontaneous locomotor activity is as an objective measure of fatigue and learned helplessness an accepted correlate of depression. We used different rat strains to evaluate stroke-induced changes in behavior in hopes that interstrain differences would provide insights into the biological basis of these symptoms. Male Lewis, Wistar, and Sprague-Dawley (SD) rats underwent experimental stroke. Spontaneous activity was assessed continually after stroke (for up to 50 days). In a subset of animals, the forced swim test was performed prior to and 1 month after stroke to assess learned helplessness; blood was obtained at sacrifice for cytokine assay. Stroke induced strain-related differences in activity; Lewis rats increased spontaneous activity during the dark cycle, while Wistar and SD rats increased activity during the light cycle. The velocity of movement decreased during the dark cycle in Wistar and SD rats and during the light cycle in Lewis rats. Stroke also led to an increase in learned helplessness in Lewis rats. In summary, different patterns of behaviors emerge in different rat strains after stroke. Lewis rats displayed behavior consistent with depression but not fatigue, while Wistar and SD rats displayed behavior consistent with fatigue but not depression. These data argue that PSF and PSD are different biological constructs and suggest that analysis of strain-related differences may provide insight into symptom pathophysiology.

Progress Report on Long Hold Time Creep Fatigue of Alloy 617 at 850°C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carroll, Laura Jill

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep-fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutes at themore » 0.3% strain range and 240 minutes at the 1.0% strain range. The creep-fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep-fatigue data are calculated for the creep-fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.« less

High Speed Research Program Sonic Fatigue

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A. (Technical Monitor); Beier, Theodor H.; Heaton, Paul

2005-01-01

The objective of this sonic fatigue summary is to provide major findings and technical results of studies, initiated in 1994, to assess sonic fatigue behavior of structure that is being considered for the High Speed Civil Transport (HSCT). High Speed Research (HSR) program objectives in the area of sonic fatigue were to predict inlet, exhaust and boundary layer acoustic loads; measure high cycle fatigue data for materials developed during the HSR program; develop advanced sonic fatigue calculation methods to reduce required conservatism in airframe designs; develop damping techniques for sonic fatigue reduction where weight effective; develop wing and fuselage sonic fatigue design requirements; and perform sonic fatigue analyses on HSCT structural concepts to provide guidance to design teams. All goals were partially achieved, but none were completed due to the premature conclusion of the HSR program. A summary of major program findings and recommendations for continued effort are included in the report.

Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

NASA Technical Reports Server (NTRS)

Phillips, E. P.

1974-01-01

Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

Management of chronic (post-viral) fatigue syndrome.

PubMed Central

Wessely, S; David, A; Butler, S; Chalder, T

1989-01-01

Simple rehabilitative strategies are proposed to help patients with the chronic fatigue syndrome. A model is outlined of an acute illness giving way to a chronic fatigue state in which symptoms are perpetuated by a cycle of inactivity, deterioration in exercise tolerance and further symptoms. This is compounded by the depressive illness that is often part of the syndrome. The result is a self-perpetuating cycle of exercise avoidance. Effective treatment depends upon an understanding of the interaction between physical and psychological factors. Cognitive behavioural therapy is suggested. Cognitive therapy helps the patient understand how genuine symptoms arise from the frequent combination of physical inactivity and depression, rather than continuing infection, while a behavioural approach enables the treatment of avoidance behaviour and a gradual return to normal physical activity. PMID:2553945

Tension-time index, fatigue, and energetics in isolated rat diaphragm: a new experimental model.

PubMed

Klawitter, Paul F; Clanton, Thomas L

2004-01-01

The tension-time index (TTI) has been used to estimate mechanical load, energy utilization, blood flow, and susceptibility to fatigue in contracting muscle. The TTI can be defined, for a rhythmically contracting muscle, as the product of average force development divided by maximum tetanic force times duty cycle [contraction time / (contraction + relaxation time)]. In this study, the TTI concept was applied to isolated diaphragm via a method that allowed TTI to be clamped at a predetermined value. The hypothesis tested was that, at constant TTI, muscle energetics and the extent of fatigue would vary with stimulation frequency. Isolated diaphragm strips were stimulated at 25, 50, 75, or 100 Hz for 4 min, one per second. Duty cycle was continuously adjusted to maintain TTI at 0.07, which was near the highest TTI tolerated for 4 min, at 20-Hz stimulation. At the end of the fatigue run, muscles were either immediately frozen for determination ATP, creatine, and creatine phosphate concentrations (n = 6) or stimulated for evaluation of low- and high-frequency fatigue (n = 5). Results demonstrated no difference in the extent of fatigue or in the final ATP and creatine phosphate concentrations between groups. Large within-run increases in duty cycle were required at low stimulation frequencies, but only small increases were required at the highest frequencies. The results demonstrate that, at a constant TTI, similar fatigue properties predominate at all stimulation frequencies with no clear distinction between high- and low-frequency fatigue. The method of clamping TTI during fatigue may be useful for evaluating energetics and contractile function between treatment groups in isolated muscle when treatment influences baseline contractile characteristics.

Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Rogers, Richard B.; Nesbitt, James A.; Puleo, Bernadette J.; Miller, Robert A.; Telesman, Ignacy; Draper, Susan L.; Locci, Ivan E.

2017-01-01

Protective ductile coatings will be necessary to mitigate oxidation and corrosion attack on superalloy disks exposed to increasing operating temperatures in some turbine engine environments. However, such coatings must be resistant to harmful surface cracking during service. The objective of this study was to investigate how residual stresses evolve in such coatings. Cylindrical gage fatigue specimens of powder metallurgy-processed disk superalloy LSHR were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of shot peening and fatigue cycling on average residual stresses and other aspects of the coating were assessed. Shot peening did induce beneficial compressive residual stresses in the coating and substrate. However, these stresses became more tensile in the coating with subsequent heating and contributed to cracking of the coating in long intervals of cycling at 760 C. Substantial compressive residual stresses remained in the substrate adjacent to the coating, sufficient to suppress fatigue cracking. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

Monitoring Poisson's Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors.

PubMed

Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S; Turkmen, Halit S; Yildiz, Mehmet

2016-09-19

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson's ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson's ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes.

Monitoring Poisson’s Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors

PubMed Central

Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S.; Turkmen, Halit S.; Yildiz, Mehmet

2016-01-01

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson’s ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson’s ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes. PMID:28773901

High temperature, low-cycle fatigue of copper-base alloys for rocket nozzles. Part 2: Strainrange partitioning and low-cycle fatigue results at 538 deg C

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1976-01-01

Low-cycle fatigue tests of 1/2 Hard AMZIRC Copper and NARloy Z were performed in argon at 538 C to determine partitioned strain range versus life relationships. Strain-controlled low-cycle fatigue tests of a Zr-Cr-Mg copper-base alloy were also performed. Strain ranges, lower than those employed in previous tests, were imposed in order to extend the fatigue life curve out to approximately 400,000 cycles. An experimental copper alloy and an experimental silver alloy were also studied. Tensile tests were performed in air at room temperature and in argon at 538 C. Strain-controlled low-cycle fatigue tests were performed at 538 C in argon to define the fatigue life over the regime from 300 to 3,000 cycles. For the silver alloy, three additional heat treatments were introduced, and a limited evaluation of the short-term tensile and low-cycle fatigue behavior at 538 C was performed.

Fatigue and Creep-Fatigue Deformation of an Ultra-Fine Precipitate Strengthened Advanced Austenitic Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

M.C. Carroll; L.J. Carroll

An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. The low-cycle fatigue and creep-fatigue behavior of an HT-UPS alloy have been investigated at 650 °C and a 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain as long as 150 min. Themore » cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in fatigue and creep-fatigue of both alloys at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present for hold times of 60 min and longer, and substantially more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ significantly; an equiaxed cellular structure is observed in 316 SS, whereas in HT-UPS the microstructure takes the form of widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as it evolves with continued cycling.« less

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei; An, Ke

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE PAGES

Wu, Wei; An, Ke

2015-10-03

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Influence of the number of cycles on shear fatigue strength of resin composite bonded to enamel and dentin using dental adhesives in self-etching mode.

PubMed

Tsujimoto, Akimasa; Barkmeier, Wayne W; Erickson, Robert L; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

2018-01-30

The influence of the number of cycles on shear fatigue strength to enamel and dentin using dental adhesives in self-etch mode was investigated. A two-step self-etch adhesive and two universal adhesives were used to bond to enamel and dentin in self-etch mode. Initial shear bond strength and shear fatigue strength to enamel and dentin using the adhesive in self-etch mode were determined. Fatigue testing was used with 20 Hz frequency and cycling periods of 50,000, 100,000 and 1,000,000 cycles, or until failure occurred. For each of the cycling periods, there was no significant difference in shear fatigue strength across the cycling periods for the individual adhesives. Differences in shear fatigue strength were found between the adhesives within the cycling periods. Regardless of the adhesive used in self-etch mode for bonding to enamel or dentin, shear fatigue strength was not influenced by the number of cycles used for shear fatigue strength testing.

Microstructure-Sensitive Modeling of High Cycle Fatigue (Preprint)

DTIC Science & Technology

2009-03-01

SUBJECT TERMS microplasticity , microstructure-sensitive modeling, high cycle fatigue, fatigue variability 16. SECURITY CLASSIFICATION OF: 17...3Air Force Research Laboratory Wright Patterson Air Force Base, Ohio 45433 Keywords: Microplasticity , microstructure-sensitive modeling, high cycle...cyclic microplasticity ) plays a key role in modeling fatigue resistance. Unlike effective properties such as elastic stiffness, fatigue is

Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weakermore » regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.« less

Fatigue Exacerbation by Interval or Continuous Exercise in Chronic Fatigue Syndrome.

PubMed

Sandler, Carolina X; Lloyd, Andrew R; Barry, Benjamin K

2016-10-01

The objective of this study is to determine whether the typical exacerbation of symptoms in patients with chronic fatigue syndrome (CFS) after a bout of exercise differs between high-intensity interval training (HIIT) or continuous (CONT) aerobic exercise of the same duration and mechanical work. Participants with specialist-diagnosed CFS performed two 20-min bouts of cycling in a randomized crossover study. The bouts were either moderate-intensity continuous (70% age-predicted HR maximum) or high-intensity interval exercise, separated by at least 2 wk. Self-report questionnaires capturing fatigue, the related symptoms, and actigraphy were collected across 2 d before and 4 d after the exercise. Comparisons between exercise bouts were made using paired sample t-tests. Fourteen moderately affected participants who were unable to work, but not bed bound, completed the study (nine female, 32 ± 10 yr, 67 ± 11 kg). Mechanical work was matched successfully between the exercise bouts (HIIT, 83,037, vs CONT, 83,348 J, P = 0.84). Mean HR (HIIT, 76% ± 5%, vs CONT, 73% ± 6% age-predicted HR maximum, P < 0.05) and RPE (6-20) in the legs (HIIT, 15.4 ± 1.4, vs CONT, 13.2 ± 1.2, P < 0.001) were higher for the interval compared with continuous exercise. Mean fatigue scores (0-10) were similar before each exercise challenge (HIIT, 4.5 ± 1.8, vs CONT, 4.1 ± 1.7, P = 0.43). Participants reported an increase in fatigue scores after both challenges (mean difference: HIIT, 1.0 ± 1.3, P < 0.01; CONT, 1.5 ± 0.7, P < 0.001), but these exacerbations in fatigue were not statistically or clinically different (P = 0.20). High-intensity interval exercise did not exacerbate fatigue any more than continuous exercise of comparable workload. This finding supports evaluation of HIIT in graded exercise therapy interventions for patients with CFS.

Draft ASME Boiler and Pressure Vessel Code Section III, Division 5, Section HB, Subsection B, Code Case for Alloy 617 and Background Documentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, Julie Knibloe

2015-08-01

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutesmore » at the 0.3% strain range and 240 minutes at the 1.0% strain range. The creep fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep fatigue data are calculated for the creep fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.« less

Low-cost directionally-solidified turbine blades, volume 2. [TFE731-3 turbofan engine

NASA Technical Reports Server (NTRS)

Dennis, R. E.; Hoppin, G. S., III; Hurst, L. G.

1979-01-01

An endothermically heated technology was used to manufacture low cost, directionally solidified, uncooled nickel-alloy blades for the TFE731-3 turbofan engine. The MAR-M 247 and MER-M 100+Hf blades were finish processed through heat treatment, machining, and coating operations prior to 150 hour engine tests consisting of the following sequences: (1) 50 hours of simulated cruise cycling (high fatigue evaluation); (2) 50 hours at the maximum continuous power rating (stress rupture endurance (low cycle fatigue). None of the blades visually showed any detrimental effects from the test. This was verified by post test metallurgical evaluation. The specific fuel consumption was reduced by 2.4% with the uncooled blades.

A Phase I study of intermittently dosed vorinostat in combination with bortezomib in patients with advanced solid tumors.

PubMed

Deming, Dustin A; Ninan, Jacob; Bailey, Howard H; Kolesar, Jill M; Eickhoff, Jens; Reid, Joel M; Ames, Matthew M; McGovern, Renee M; Alberti, Dona; Marnocha, Rebecca; Espinoza-Delgado, Igor; Wright, John; Wilding, George; Schelman, William R

2014-04-01

Accumulating evidence shows evidence of efficacy with the combination of vorinostat and bortezomib in solid tumors. We previously examined a once-daily continuous dosing schedule of vorinostat in combination with bortezomib which was well tolerated in cycles 1 and 2; however, there was concern regarding the tolerability through multiple cycles. This study was conducted to evaluate an intermittent dosing schedule of vorinostat with bortezomib. Vorinostat was initially administered orally twice daily on days 1-14 with bortezomib IV on days 1, 4, 8, and 11 of a 21 day cycle. Two DLTs (elevated ALT and fatigue) were observed at dose level 1, thus the protocol was amended to administer vorinostat intermittently twice daily on days 1-4 and 8-11. 29 patients were enrolled; 13 men and 16 women. Common cancer types included sarcoma, pancreatic, colorectal, GIST, and breast. The most common Grade 3-4 toxicities at any dose level included thrombocytopenia, fatigue, increased ALT, elevated INR, and diarrhea. DLTs in the intermittent dosing scheduled included thrombocytopenia and fatigue. The Cmax and AUC for the intermittent dosing regimen were similar to those observed in the daily dosing. In this heavily pretreated population, stable disease was observed in patients with sarcoma, colorectal adenocarcinoma and GIST. The MTD was established at vorinostat 300 mg BID on days 1-4 and 8-11 and bortezomib 1.3 mg/m(2) IV on days 1, 4, 8, and 11 of a 21 day cycle. Tolerability was not improved with the intermittent dosing schedule of vorinostat when compared to continuous dosing.

Effect of mission cycling on the fatigue performance of SiC-coated carbon-carbon composites

NASA Technical Reports Server (NTRS)

Mahfuz, H.; Das, P. S.; Jeelani, S.; Baker, D. M.; Johnson, S. A.

1993-01-01

The effects of thermal and pressure cycling on the fatigue performance of carbon-carbon composites, and the influence of mission cycling on these effects, were investigated by subjecting both virgin and mission-cycled two-dimensional specimens of SiC-coated carbon-carbon composites to fatigue tests, conducted at room temperature in three-point bending, with a stress ratio of 0.2 and a frequency of 1 Hz. It was found that the fatigue strength of C-C composites is high (about 90 percent of the ultimate flexural strength), but decreased with the mission cycling. The lowering of the fatigue strength with mission cycling is attributed to the increase in interfacial bond strength due to thermal and pressure cycling of the material. The already high sensitivity of C-C composites to stress during cyclic loading increases further with the amount of mission cycling. Results of NDE suggest that the damage growth in virgin C-C, in the high-cycle range, is slow at the initial stage of the cyclic life, but propagates rapidly after certain threshold cycles of the fatigue life.

Fatigue limit and Hysteresis Behavior of Type 304L Stainless Steel in Air and PWR Water, at 150°C and 300°C

NASA Astrophysics Data System (ADS)

Solomon, H. D.; Amzallag, C.; Vallee, A. J.; DeLair, R. E.

This is a study of the 107 cycle fatigue limit of Type 304L Stainless Steel, as measured in fully reversed (R=-1) load-controlled tests, at 150°C and 300°C, in air and PWR water. The staircase method was used to determine the fatigue limit. The tests run here utilized a cycle frequency of 1.818Hz and are compared to other tests from the literature that were run at 30Hz. The fatigue limit measured in the tests run at the high frequency was higher than that measured here. This is explained by measurements of the strain developed during cycling, using the different cycle frequencies. The tests run at the higher frequencies yielded lower strains for a given stress and, as expected, this resulted in higher fatigue limits. Using 107 cycles to define a run-out also led to a lower fatigue limit. These results are important as most previous fatigue limit measurements utilized 106 cycles or less to define a run-out, and when lives as long as 107 cycles are used the tests are generally run at high cycle frequencies, thus leading to higher fatigue limits than those measured here.

In situ SEM thermal fatigue of Al/graphite metal matrix composites

NASA Technical Reports Server (NTRS)

Zong, G. S.; Rabenberg, L.; Marcus, H. L.

1990-01-01

Several thermal fatigue-induced failure mechanisms are deduced for unidirectional graphite-reinforced 6061 Al-alloy MMCs subjected to in situ thermal cycling. These thermal cycling conditions are representative of MMC service cycles in aerospace environments, where thermal fatigue is primarily associated with changes in the stress states near the interfaces due to coefficient of thermal expansion mismatch between fiber and matrix. This in situ SEM thermal-cycling study clarified such factors affecting MMCs' thermal fatigue as local fiber content and distribution, void volume, fiber stiffness, thermal excursion magnitude, and number of thermal cycles. MMC microfailure modes in thermal fatigue have been deduced.

High temperature, low cycle fatigue of copper-base alloys in argon. Part 3: Zirconium-copper; thermal-mechanical strain cycling, hold-time and notch fatigue results

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

The low-cycle fatigue characteristics of smooth bar and notched bar specimens (hourglass shape) of zirconium-copper, 1/2 Hard, material (R-2 Series) were evaluated at room temperature in axial strain control. Over the fatigue life range from about 300 to 3000 cycles the ratio of fatigue life for smooth bar to fatigue life for notched bar remained constant at a value of about 6.0. Some additional hold-time data for the R-2 alloy tested in argon at 538 C are reported. An analysis of the relaxation data obtained in these hold-time tests is also reported and it is shown that these data yield a fairly consistent correlation in terms of instantaneous stress rate divided by instantaneous stress. Two thermal-mechanical strain cycling tests were also performed using a cyclic frequency of 4.5 cycles per hour and a temperature cycling interval from 260 to 538 C. The fatigue life values in these tests were noticeably lower than that observed in isothermal tests at 538 C.

Effect of Pre-Strain on the Fatigue Behavior of Extruded AZ31 Alloys

NASA Astrophysics Data System (ADS)

Wu, Yanjun

2017-09-01

An attempt is made to rationalize the effect of pre-strain history on fatigue behaviors of AZ31 magnesium alloy. Axial fatigue tests were conducted in the extruded and pre-compressioned AZ31 alloy under low cycle total strain control fatigue conditions. The pre-strain process influences the plastic deformation mechanism activated during fatigue deformation, especially during tensile loading, by enhancing the activity of detwinning mechanism. The low-cycle fatigue lifetime of extruded AZ31 alloy can be enhanced by the pre-compression process. And the hysteresis energy was successfully used to predict the low-cycle fatigue lifetime.

Investigation into Fretting Fatigue Under Cyclic Contact Load and in Conjunction with Plain Fatigue of Titanium Alloy

DTIC Science & Technology

2008-03-01

by plain fatigue and the process kept alternating or finishing all fretting fatigue cycles first followed by plain fatigue...fatigue and the process kept alternating or finishing all fretting fatigue cycles first followed by plain fatigue. 127  6.2.2. Phase Difference...component’s life. Figure 1.2 illustrates the process of combination of fretting fatigue and plain fatigue, by using three parts. The first part of this figure

Effect of welding structure and δ-ferrite on fatigue properties for TIG welded austenitic stainless steels at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Yuri, Tetsumi; Ogata, Toshio; Saito, Masahiro; Hirayama, Yoshiaki

2000-04-01

High-cycle and low-cycle fatigue properties of base and weld metals for SUS304L and SUS316L and the effects of welding structure and δ-ferrite on fatigue properties were investigated at cryogenic temperatures in order to evaluate the long-life reliability of the structural materials to be used in liquid hydrogen supertankers and storage tanks and to develop a welding process for these applications. The S-N curves of the base and weld metals shifted towards higher levels, i.e., the longer life side, with decreasing test temperatures. High-cycle fatigue tests demonstrated the ratios of fatigue strength at 10 6 cycles to tensile strength of the weld metals to be 0.35-0.7, falling below those of base metals with decreasing test temperatures. Fatigue crack initiation sites in SUS304L weld metals were mostly at blowholes with diameters of 200-700 μm, and those of SUS316L weld metals were at weld pass interface boundaries. Low-cycle fatigue tests revealed the fatigue lives of the weld metals to be somewhat lower than those of the base metals. Although δ-ferrite reduces the toughness of austenitic stainless steels at cryogenic temperatures, the effects of δ-ferrite on high-cycle and low-cycle fatigue properties are not clear or significant.

Temperature effects on the strainrange partitioning approach for creep-fatigue analysis

NASA Technical Reports Server (NTRS)

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

1972-01-01

Examination is made of the influence of temperature on the strainrange partitioning approach to creep-fatigue. Results for Cr-Mo steel and Type 316 stainless steel show the four partitioned strainrange-life relationships to be temperature insensitive to within a factor of two on cyclic life. Monotonic creep and tensile ductilities were also found to be temperature insensitive to within a factor of two. The approach provides bounds on cyclic life that can be readily established for any type of inelastic strain cycle. Continuous strain cycling results obtained over a broad range of high temperatures and frequencies are in excellent agreement with bounds provided by the approach. The observed transition from one bound to the other is also in good agreement with the approach.

Fatigue of die cast zinc alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schrems, K.K.; Dogan, O.N.; Goodwin, F.E.

2006-04-01

The rotating bending fatigue limit of die cast zinc alloy 2, alloy 3, alloy 5, AcuZinc 5, and ZA-8 were determined as a part of an on-going program by ILZRO into the mechanical properties of die cast zinc. The stress-life (S-N) curves of alloys 3, 5, AcuZinc 5, and ZA-8 were determined previously. This presentation reports the results of the S-N curve for Alloy 2 and the calculated fatigue limits for all five alloys. During the previous stress-life testing, the samples were stopped at 10 million cycles and the fatigue limit for alloy 3, alloy 5, and AcuZinc 5 appearedmore » to be higher and the fatigue limit for ZA-8 appeared to be lower than the values reported in the literature. This was further investigated in alloy 5 and ZA-8 by testing continuous cast bulk alloy 5 and ZA-8.« less

High-Cycle, Push-Pull Fatigue Fracture Behavior of High-C, Si-Al-Rich Nanostructured Bainite Steel.

PubMed

Zhao, Jing; Ji, Honghong; Wang, Tiansheng

2017-12-29

The high-cycle, push-pull fatigue fracture behavior of high-C, Si-Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push-pull fatigue limits at 10⁷ cycles were estimated as 710-889 MPa, for the samples isothermally transformed at the temperature range of 220-260 °C through data extrapolation, measured under the maximum cycle number of 10⁵. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite.

High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

PubMed Central

Zhao, Jing; Ji, Honghong

2017-01-01

The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite. PMID:29286325

Technical evaluation report of the Specialists Meeting on Characterization of Low Cycle High Temperature Fatigue by the Strainrange Partitioning Method

NASA Technical Reports Server (NTRS)

Drapier, J. M.; Hirschberg, M. H.

1979-01-01

The ability of the Strainrange Partitioning Method SRP was evaluated to correlate the creep-fatigue behavior of gas turbine materials and to predict the creep fatigue life of laboratory specimens subjected to complex cycling conditions. A reference body of high temperature creep fatigue data which can be used in the evaluation of other SRP and low cycle high temperature fatigue predictive techniques was provided.

High-Cycle Fatigue of High-Strength Low Alloy Steel Q345 Subjected to Immersion Corrosion for Mining Wheel Applications

NASA Astrophysics Data System (ADS)

Dicecco, Sante; Altenhof, William; Hu, Henry; Banting, Richard

2017-04-01

In an effort to better understand the impact of material degradation on the fatigue life of mining wheels made of a high-strength low alloy carbon steel (Q345), this study seeks to evaluate the effect of surface corrosion on the high-cycle fatigue behavior of the Q345 alloy. The fatigue behavior of the polished and corroded alloy was investigated. Following exposure to a 3.5 wt.% NaCl saltwater solution, polished and corroded fatigue specimens were tested using an R.R. Moore rotating-bending fatigue apparatus. Microstructural analyses via both optical microscopy and scanning electron microscopy (SEM) revealed that one major phase, α-iron phase, ferrite, and one minor phase, colony pearlite, existed in the extracted Q345 alloy. The results of the fatigue testing showed that the polished and corroded specimens had an endurance strength of approximately 295 and 222 MPa, respectively, at 5,000,000 cycles. The corroded surface condition resulted in a decrease in the fatigue strength of the Q345 alloy by 24.6%. Scanning electron microscope fractography indicated that failure modes for polished and corroded fatigue specimens were consistent in the high-cycle low loading fatigue regime. Conversely, SEM fractography of low-cycle high-loading fatigue specimens found considerable differences in fracture surfaces between the corroded and polished fatigue specimens.

The relationship between fatigue and light exposure during chemotherapy.

PubMed

Liu, Lianqi; Marler, Matthew R; Parker, Barbara A; Jones, Vicky; Johnson, Sherella; Cohen-Zion, Mairav; Fiorentino, Lavinia; Sadler, Georgia Robins; Ancoli-Israel, Sonia

2005-12-01

Fatigue is one of the most common and distressing complaints among cancer patients, not only during radiation and chemotherapy, but also for months to years after the completion of treatment. Fatigue interferes with patients' daily lives, reduces their quality of life, and is often a significant reason why patients discontinue treatment. We hypothesized that some of the fatigue may be related to disrupted circadian rhythms and low light exposure. The main objective of this study therefore was to investigate the association between fatigue and light exposure among patients with breast cancer. As part of a larger, ongoing prospective study on fatigue, sleep, and circadian rhythms in patients with breast cancer, an analysis of 63 women newly diagnosed with stage I-IIIA breast cancer and scheduled to receive four cycles of adjuvant or neoadjuvant anthracycline-based chemotherapy was conducted. Data were collected before and during weeks 1, 2, and 3 of cycle 1 and cycle 4. Fatigue was assessed using the Short Form of Multidimensional Fatigue Symptom Inventory. Light exposure was recorded with a wrist actigraph. There were significant correlations between fatigue levels and light exposure (r=-0.28 to -0.45) within both cycle 1 and cycle 4, such that higher levels of fatigue were associated with less light exposure. There were also significant correlations between changes in light exposure and changes in fatigue within the first 2 weeks of each cycle (r=-0.28 to -0.52). Increased fatigue was significantly correlated with decreased light exposure among patients with breast cancer. Although the cause and effect of exacerbated fatigue and decreased light exposure cannot be confirmed by the current study, and lower light exposure may just in part be due to the fatigued patients spending less time outdoors in bright light, two hypotheses are proposed about the mechanisms by which light may alleviate the fatigue of patients with breast cancer. These results suggest the need for prospective intervention studies of light therapy for breast-cancer-related fatigue.

Understanding the Reliability of Solder Joints Used in Advanced Structural and Electronics Applications: Part 2 - Reliability Performance.

DOE PAGES

Vianco, Paul T.

2017-03-01

Whether structural or electronic, all solder joints must provide the necessary level of reliability for the application. The Part 1 report examined the effects of filler metal properties and the soldering process on joint reliability. Filler metal solderability and mechanical properties, as well as the extents of base material dissolution and interface reaction that occur during the soldering process, were shown to affect reliability performance. The continuation of this discussion is presented in this Part 2 report, which highlights those factors that directly affect solder joint reliability. There is the growth of an intermetallic compound (IMC) reaction layer at themore » solder/base material interface by means of solid-state diffusion processes. In terms of mechanical response by the solder joint, fatigue remains as the foremost concern for long-term performance. Thermal mechanical fatigue (TMF), a form of low-cycle fatigue (LCF), occurs when temperature cycling is combined with mismatched values of the coefficient of thermal expansion (CTE) between materials comprising the solder joint “system.” Vibration environments give rise to high-cycle fatigue (HCF) degradation. Although accelerated aging studies provide valuable empirical data, too many variants of filler metals, base materials, joint geometries, and service environments are forcing design engineers to embrace computational modeling to predict the long-term reliability of solder joints.« less

Investigation of Cumulative Fatigue Damage Through Sequential Low Cycle Fatigue and High Cycle Fatigue Cycling at High Temperature for a Type 316LN Stainless Steel: Life-Prediction Techniques and Associated Mechanisms

NASA Astrophysics Data System (ADS)

Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Laha, K.; Okazaki, M.

2017-03-01

Cumulative fatigue damage under sequential low cycle fatigue (LCF) and high cycle fatigue (HCF) cycling was investigated at 923 K (650 °C) by conducting HCF tests on specimens subjected to prior LCF cycling at various strain amplitudes. Remnant HCF lives were found to decrease drastically with increase in prior fatigue exposure as a result of strong LCF-HCF interactions. The rate of decrease in remnant lives varied as a function of the applied strain amplitude. A threshold damage in terms of prior LCF life-fraction was found, below which no significant LCF-HCF interaction takes place. Similarly, a critical damage during the LCF pre-cycling marking the highest degree of LCF-HCF interaction was identified which was found to depend on the applied strain amplitude. In view of the non-linear damage accumulation behavior, Miner's linear damage rule proved to be highly non-conservative. Manson's damage curve approach, suitably modified, was found to be a better alternative for predicting the remnant HCF life. The single constant ( β) employed in the model, which reflects the damage accumulation of the material under two/multi-level loading conditions is derived from the regression analysis of the experimental results and validated further.

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

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Miller, Robert A.

1997-01-01

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

Fatigue crack growth and low cycle fatigue of two nickel base superalloys

NASA Technical Reports Server (NTRS)

Stoloff, N. S.; Duquette, D. J.; Choe, S. J.; Golwalkar, S.

1983-01-01

The fatigue crack growth and low cycle fatigue behavior of two P/M superalloys, Rene 95 and Astroloy, in the hot isostatically pressed (HIP) condition, was determined. Test variables included frequency, temperature, environment, and hold times at peak tensile loads (or strains). Crack initiation sites were identified in both alloys. Crack growth rates were shown to increase in argon with decreasing frequency or with the imposition of hold times. This behavior was attributed to the effect of oxygen in the argon. Auger analyses were performed on oxide films formed in argon. Low cycle fatigue lives also were degraded by tensile hold, contrary to previous reports in the literature. The role of environment in low cycle fatigue behavior is discussed.

The numerical high cycle fatigue damage model of fillet weld joint under weld-induced residual stresses

NASA Astrophysics Data System (ADS)

Nguyen Van Do, Vuong

2018-04-01

In this study, a development of nonlinear continuum damage mechanics (CDM) model for multiaxial high cycle fatigue is proposed in which the cyclic plasticity constitutive model has been incorporated in the finite element (FE) framework. T-joint FE simulation of fillet welding is implemented to characterize sequentially coupled three-dimensional (3-D) of thermo-mechanical FE formulation and simulate the welding residual stresses. The high cycle fatigue damage model is then taken account into the fillet weld joints under the various cyclic fatigue load types to calculate the fatigue life considering the residual stresses. The fatigue crack initiation and the propagation in the present model estimated for the total fatigue is compared with the experimental results. The FE results illustrated that the proposed high cycle fatigue damage model in this study could become a powerful tool to effectively predict the fatigue life of the welds. Parametric studies in this work are also demonstrated that the welding residual stresses cannot be ignored in the computation of the fatigue life of welded structures.

A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue

NASA Technical Reports Server (NTRS)

Romanoski, Glenn R.; Pelloux, Regis M.; Antolovich, Stephen D.

1988-01-01

Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.

Cyclic fatigue resistance of ProTaper Universal instruments when subjected to static and dynamic tests.

PubMed

Lopes, Hélio P; Britto, Izabelle M O; Elias, Carlos N; Machado de Oliveira, Julio C; Neves, Mônica A S; Moreira, Edson J L; Siqueira, José F

2010-09-01

This study evaluated the number of cycles to fracture of ProTaper Universal S2 instruments when subjected to static and dynamic cyclic fatigue tests. ProTaper Universal S2 instruments were used until fracture in an artificial curved canal under rotational speed of 300 rpm in either a static or a dynamic test model. Afterward, the length of the fractured segments was measured and fractured surfaces and helical shafts analyzed by scanning electron microscopy (SEM). The number of cycles to fracture was significantly increased when instruments were tested in the dynamic model (P<.001). Instrument separation occurred at the point of maximum flexure within the artificial canals, i.e., the midpoint of the curved canal segment. SEM analysis revealed that fractured surfaces exhibited characteristics of the ductile mode. Plastic deformation was not observed in the helical shaft of fractured instruments. The number of cycles to fracture ProTaper Universal S2 instruments significantly increased with the use of instruments in a dynamic cyclic fatigue test compared with a static model. These findings reinforce the need for performing continuous pecking motions during rotary instrumentation of curved root canals. Copyright (c) 2010 Mosby, Inc. All rights reserved.

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior

NASA Technical Reports Server (NTRS)

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

1986-01-01

The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.

A systems approach to solder joint fatigue in spacecraft electronic packaging

NASA Technical Reports Server (NTRS)

Ross, R. G., Jr.

1991-01-01

Differential expansion induced fatigue resulting from temperature cycling is a leading cause of solder joint failures in spacecraft. Achieving high reliability flight hardware requires that each element of the fatigue issue be addressed carefully. This includes defining the complete thermal-cycle environment to be experienced by the hardware, developing electronic packaging concepts that are consistent with the defined environments, and validating the completed designs with a thorough qualification and acceptance test program. This paper describes a useful systems approach to solder fatigue based principally on the fundamental log-strain versus log-cycles-to-failure behavior of fatigue. This fundamental behavior has been useful to integrate diverse ground test and flight operational thermal-cycle environments into a unified electronics design approach. Each element of the approach reflects both the mechanism physics that control solder fatigue, as well as the practical realities of the hardware build, test, delivery, and application cycle.

An investigation of strain cycling behavior of 7075-T6 aluminum under combined state of strain: The effects of out-of-phase, biaxial strain cycling on low cycle fatigue

NASA Technical Reports Server (NTRS)

Zamrik, S. Y.

1972-01-01

The effect of out-of-phase strain cycling on the low cycle fatigue of biaxially loaded specimens is discussed. A method to apply phase angles between two strains imposed in two different directions was developed. The data and the proposed theoretical analysis are part of a research program on biaxial strain cycling effect on fatigue life of structural materials.

Types of rotor failure and characteristics of fragments

NASA Technical Reports Server (NTRS)

Mccarthy, D.

1977-01-01

Noncontained rotor failures in U.K. engines resulting from low cycle fatigue, low cycle fatigue with superimposed high cycle fatigue, and overheating and-or overspeeding were analyzed. The size, shape, weight, velocity, energy, and direction of the fragments released from turbines and compressors were studied and are presented in graph.

Investigation of the High-Cycle Fatigue Life of Selective Laser Melted and Hot Isostatically Pressed Ti-6Al-4v

DTIC Science & Technology

2015-03-26

INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V THESIS Kevin D. Rekedal...ENY-MS-15-M-212 INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V THESIS...AFIT-ENY-MS-15-M-212 INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V

A Mechanistic Thermal Fatigue Model for SnAgCu Solder Joints

NASA Astrophysics Data System (ADS)

Borgesen, Peter; Wentlent, Luke; Hamasha, Sa'd.; Khasawneh, Saif; Shirazi, Sam; Schmitz, Debora; Alghoul, Thaer; Greene, Chris; Yin, Liang

2018-02-01

The present work offers both a complete, quantitative model and a conservative acceleration factor expression for the life span of SnAgCu solder joints in thermal cycling. A broad range of thermal cycling experiments, conducted over many years, has revealed a series of systematic trends that are not compatible with common damage functions or constitutive relations. Complementary mechanical testing and systematic studies of the evolution of the microstructure and damage have led to a fundamental understanding of the progression of thermal fatigue and failure. A special experiment was developed to allow the effective deconstruction of conventional thermal cycling experiments and the finalization of our model. According to this model, the evolution of damage and failure in thermal cycling is controlled by a continuous recrystallization process which is dominated by the coalescence and rotation of dislocation cell structures continuously added to during the high-temperature dwell. The dominance of this dynamic recrystallization contribution is not consistent with the common assumption of a correlation between the number of cycles to failure and the total work done on the solder joint in question in each cycle. It is, however, consistent with an apparent dependence on the work done during the high-temperature dwell. Importantly, the onset of this recrystallization is delayed by pinning on the Ag3Sn precipitates until these have coarsened sufficiently, leading to a model with two terms where one tends to dominate in service and the other in accelerated thermal cycling tests. Accumulation of damage under realistic service conditions with varying dwell temperatures and times is also addressed.

Influence of creep damage on the low cycle thermal-mechanical fatigue behavior of two tantalum base alloys

NASA Technical Reports Server (NTRS)

Sheffler, K. D.; Doble, G. S.

1972-01-01

Low cycle fatigue tests have been performed on the tantalum base alloys T-111 and ASTAR 811C with synchronized, independently programmed temperature and strain cycling. The thermal-mechanical cycles applied fell into three basic categories: these were isothermal cycling, in-phase thermal cycling, and out-of-phase thermal cycling. In-phase cycling was defined as tensile deformation associated with high temperature and compressive deformation with low temperature, while out-of-phase thermal cycling was defined as the reverse case. The in-phase thermal cycling had a pronounced detrimental influence on the fatigue life of both alloys, with the life reduction being greater in the solid solution strengthened T-111 alloy than in the carbide strengthened ASTAR 811C alloy. The out-of-phase tests also showed pronounced effects on the fatigue life of both alloys, although not as dramatic.

High-temperature, low-cycle fatigue behavior of an Al-Mg-Si based heat-resistant aluminum alloy

NASA Astrophysics Data System (ADS)

Kim, Kyu-Sik; Sung, Si-Young; Han, Bum-Suck; Park, Joong-Cheol; Lee, Kee-Ahn

2015-11-01

High-temperature, low-cycle fatigue behavior of the new heat-resistant aluminum alloy was investigated in this study. The aluminum alloy consists of aluminum matrix and small amount of precipitated Mg2Si and (Co, Ni)3Al4 strengthening particles. At room temperature and 523 K, the yield and tensile strengths of Al-Mg-Si-(Co, Ni) the aluminum alloy were maintained with no significant decrease, and elongation increased slightly. Low-cycle fatigue tests controlled by total strain were performed with strain ratio (R) = -1, strain rate = 2×10-3 s-1 at 523 K. The fatigue limit of the low-cycle fatigue of this alloy showed plastic strain amplitude (Δ ɛ pa) of 0.22% at 103 cycles. This value was superior to that of conventional aluminum alloy such as A319. The results of the fractographical observation showed that second phases, especially (Co, Ni)3Al4 particles, affected fatigue behavior. This study also attempted to clarify the mechanism of high-temperature, low-cycle fatigue deformation of Al-Mg-Si-(Co, Ni) alloy in relation to its microstructure and energy dissipation analysis.

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

NASA Astrophysics Data System (ADS)

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

2015-02-01

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

Gamma Radiation Sterilization Reduces the High-cycle Fatigue Life of Allograft Bone.

PubMed

Islam, Anowarul; Chapin, Katherine; Moore, Emily; Ford, Joel; Rimnac, Clare; Akkus, Ozan

2016-03-01

Sterilization by gamma radiation impairs the mechanical properties of bone allografts. Previous work related to radiation-induced embrittlement of bone tissue has been limited mostly to monotonic testing which does not necessarily predict the high-cycle fatigue life of allografts in vivo. We designed a custom rotating-bending fatigue device to answer the following questions: (1) Does gamma radiation sterilization affect the high-cycle fatigue behavior of cortical bone; and (2) how does the fatigue life change with cyclic stress level? The high-cycle fatigue behavior of human cortical bone specimens was examined at stress levels related to physiologic levels using a custom-designed rotating-bending fatigue device. Test specimens were distributed among two treatment groups (n = 6/group); control and irradiated. Samples were tested until failure at stress levels of 25, 35, and 45 MPa. At 25 MPa, 83% of control samples survived 30 million cycles (run-out) whereas 83% of irradiated samples survived only 0.5 million cycles. At 35 MPa, irradiated samples showed an approximately 19-fold reduction in fatigue life compared with control samples (12.2 × 10(6) ± 12.3 × 10(6) versus 6.38 × 10(5) ± 6.81 × 10(5); p = 0.046), and in the case of 45 MPa, this reduction was approximately 17.5-fold (7.31 × 10(5) ± 6.39 × 10(5) versus 4.17 × 10(4) ± 1.91 × 10(4); p = 0.025). Equations to estimate high-cycle fatigue life of irradiated and control cortical bone allograft at a certain stress level were derived. Gamma radiation sterilization severely impairs the high cycle fatigue life of structural allograft bone tissues, more so than the decline that has been reported for monotonic mechanical properties. Therefore, clinicians need to be conservative in the expectation of the fatigue life of structural allograft bone tissues. Methods to preserve the fatigue strength of nonirradiated allograft bone tissue are needed. As opposed to what monotonic tests might suggest, the cyclic fatigue life of radiation-sterilized structural allografts is likely severely compromised relative to the nonirradiated condition and therefore should be taken into consideration. Methods to reduce the effect of irradiation or to recover structural allograft bone tissue fatigue strength are important to pursue.

Probabilistic material strength degradation model for Inconel 718 components subjected to high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue effects

NASA Technical Reports Server (NTRS)

Bast, Callie C.; Boyce, Lola

1995-01-01

This report presents the results of both the fifth and sixth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA). The research included on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for five variables, namely, high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using an updated version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of high-cycle mechanical fatigue, creep and thermal fatigue was performed. Then using the current version of PROMISS, entitled PROMISS94, a second sensitivity study including the effect of low-cycle mechanical fatigue, as well as, the three previous effects was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of high-cycle mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

Effects of caffeine ingestion on endurance performance in mentally fatigued individuals.

PubMed

Azevedo, Rafael; Silva-Cavalcante, Marcos David; Gualano, Bruno; Lima-Silva, Adriano E; Bertuzzi, Romulo

2016-12-01

To examine the effects of caffeine ingestion on physiological and perceptual responses in mentally fatigued individuals. Eight male physically active subjects completed four cycling constant-workload tests in four experimental conditions at 80 % of maximal power output: control (C), mental fatigue (MF), mental fatigue plus caffeine ingestion (5 mg/kg) (MF-CAF), and mental fatigue plus placebo (MF-PLA). The mental fatigue was induced by a continuous performance task A-X version (AX-CPT). Before and after the AX-CPT, the profile of mood state (POMS) and blood samples for lactate measurement were collected. Oxygen consumption ([Formula: see text]), rating of perceived exertion (RPE), and electromyography (EMG) activity were measured during the cycling test. The time to exhaustion in C, MF, MF-PLA, and MF-CAF were 251 ± 30, 222 ± 23, 248 ± 28, and 285 ± 42 s, respectively. Delta values (corrected by C condition) were higher in MF-CAF than MF (P = 0.031). MF-CAF reported higher Vigor scores when compared with C (P = 0.046) and MF (P = 0.020). RPE at the first minute was significantly higher in MF-PLA than in C (P = 0.050); at the second minute, RPE was higher in MF-PLA than in C (P = 0.049) and MF-CAF (P = 0.048). EMG activity was not different between the conditions. Caffeine ingestion increased approximately 14 % endurance performance after the induction of mental fatigue. This effect was accompanied by a tendency to improvement in mood state (i.e., vigor). Therefore, caffeine ingestion can promote a beneficial effect on endurance performance in mentally fatigued individuals.

Cumulative fatigue damage behavior of MAR M-247

NASA Technical Reports Server (NTRS)

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

1991-01-01

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

Fatigue crack tip deformation and fatigue crack propagation

NASA Technical Reports Server (NTRS)

Kang, T. S.; Liu, H. W.

1972-01-01

The effects of stress ratio, prestress cycling and plate thickness on the fatigue crack propagation rate are studied on 2024-T351 aluminum alloy. Fatigue crack propagation rate increases with the plate thickness and the stress ratio. Prestress cycling below the static yield strength has no noticeable effect on the fatigue crack propagation rate. However, prestress cycling above the static yield strength causes the material to strain harden and increases the fatigue crack propagation rate. Crack tip deformation is used to study the fatigue crack propagation. The crack tip strains and the crack opening displacements were measured from moire fringe patterns. The moire fringe patterns were obtained by a double exposure technique, using a very high density master grille (13,400 lines per inch).

Elevated Temperature Fatigue Endurance of Three Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Verrilli, Michael J.

2007-01-01

High-cycle fatigue endurance of three candidate materials for the acoustic liners of the Enabling Propulsion Materials Nozzle Program was investigated. The ceramic matrix composite materials investigated were N720/AS (Nextel 720, 3M Corporation), Sylramic S200 (Dow Corning), and UT 22. High-cycle fatigue tests were conducted in air at 910 C on as-machined specimens and on specimens subjected to tensile cyclic load excursions every 160 hr followed by thermal exposure at 910 C in a furnace up to total exposure times of 2066 and 4000 hr. All the fatigue tests were conducted in air at 100 Hz with a servohydraulic test machine. In the as-machined condition, among the three materials investigated only the Sylramic S200 exhibited a deterministic type of high-cycle fatigue behavior. Both the N720/AS and UT-22 exhibited significant scatter in the experimentally observed high-cycle fatigue lives. Among the thermally exposed specimens, N720/AS and Sylramic S200 materials exhibited a reduction in the high-cycle fatigue lives, particularly at the exposure time of 4000 hr.

Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

NASA Technical Reports Server (NTRS)

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

2002-01-01

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

Low cycle fatigue numerical estimation of a high pressure turbine disc for the AL-31F jet engine

NASA Astrophysics Data System (ADS)

Spodniak, Miroslav; Klimko, Marek; Hocko, Marián; Žitek, Pavel

This article deals with the description of an approximate numerical estimation approach of a low cycle fatigue of a high pressure turbine disc for the AL-31F turbofan jet engine. The numerical estimation is based on the finite element method carried out in the SolidWorks software. The low cycle fatigue assessment of a high pressure turbine disc was carried out on the basis of dimensional, shape and material disc characteristics, which are available for the particular high pressure engine turbine. The method described here enables relatively fast setting of economically feasible low cycle fatigue of the assessed high pressure turbine disc using a commercially available software. The numerical estimation of accuracy of a low cycle fatigue depends on the accuracy of required input data for the particular investigated object.

Effects of the Electron Beam Welding Process on the Microstructure, Tensile, Fatigue and Fracture Properties of Nickel Alloy Nimonic 80A

NASA Astrophysics Data System (ADS)

Zhang, H.; Huang, Chongxiang; Guan, Zhongwei; Li, Jiukai; Liu, Yongjie; Chen, Ronghua; Wang, Qingyuan

2018-01-01

The purpose of this study was to evaluate rotary bending high-cycle fatigue properties and crack growth of Nimonic 80A-based metal and electron beam-welded joints. All the tests were performed at room temperature. Fracture surfaces under high-cycle fatigue and fatigue crack growth were observed by scanning electron microscopy. Microstructure, hardness and tensile properties were also evaluated in order to understand the effects on the fatigue results obtained. It was found that the tensile properties, hardness and high-cycle fatigue properties of the welded joint are lower than the base metal. The fracture surface of the high-cycle fatigue shows that fatigue crack initiated from the surface under the high stress amplitude and from the subsurface under the low stress amplitude. The effect of the welding process on the statistical fatigue data was studied with a special focus on probabilistic life prediction and probabilistic lifetime limits. The fatigue crack growth rate versus stress intensity factor range data were obtained from the fatigue crack growth tests. From the results, it was evident that the fatigue crack growth rates of the welded are higher than the base metal. The mechanisms and fracture modes of fatigue crack growth of welded specimens were found to be related to the stress intensity factor range ΔK. In addition, the effective fatigue crack propagation thresholds and mismatch of welded joints were described and discussed.

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

NASA Technical Reports Server (NTRS)

Bast, Callie C.; Boyce, Lola

1995-01-01

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

A Cycling Movement Based System for Real-Time Muscle Fatigue and Cardiac Stress Monitoring and Analysis

PubMed Central

Chen, Szi-Wen; Liaw, Jiunn-Woei; Chang, Ya-Ju; Chan, Hsiao-Lung; Chiu, Li-Yu

2015-01-01

In this study, we defined a new parameter, referred to as the cardiac stress index (CSI), using a nonlinear detrended fluctuation analysis (DFA) of heart rate (HR). Our study aimed to incorporate the CSI into a cycling based fatigue monitoring system developed in our previous work so the muscle fatigue and cardiac stress can be both continuously and quantitatively assessed for subjects undergoing the cycling exercise. By collecting electrocardiogram (ECG) signals, the DFA scaling exponent α was evaluated on the RR time series extracted from a windowed ECG segment. We then obtained the running estimate of α by shifting a one-minute window by a step of 20 seconds so the CSI, defined as the percentage of all the less-than-one α values, can be synchronously updated every 20 seconds. Since the rating of perceived exertion (RPE) scale is considered as a convenient index which is commonly used to monitor subjective perceived exercise intensity, we then related the Borg RPE scale value to the CSI in order to investigate and quantitatively characterize the relationship between exercise-induced fatigue and cardiac stress. Twenty-two young healthy participants were recruited in our study. Each participant was asked to maintain a fixed pedaling speed at a constant load during the cycling exercise. Experimental results showed that a decrease in DFA scaling exponent α or an increase in CSI was observed during the exercise. In addition, the Borg RPE scale and CSI were positively correlated, suggesting that the factors due to cardiac stress might also contribute to fatigue state during physical exercise. Since the CSI can effectively quantify the cardiac stress status during physical exercise, our system may be used in sports medicine, or used by cardiologists who carried out stress tests for monitoring heart condition in patients with heart diseases. PMID:26115515

Crack Initiation and Growth Behavior at Corrosion Pit in 2024-T3 Aluminum Alloy

DTIC Science & Technology

2014-09-01

63 Figure B.1: The crack length vs. number of cycles during fatigue testing for the 2AI-01 specimen...number of cycles during fatigue testing for the the 2AI- 02 specimen...64 Figure B.3: The crack length vs. number of cycles during fatigue testing for the 2Sl-01 specimen

Crack propagation at stresses below the fatigue limit.

NASA Technical Reports Server (NTRS)

Holden, F. C.; Hyler, W. S.; Marschall, C. W.

1967-01-01

Crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting of alternating stress cycles crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting role of alternating stress cycles

Multiscale Fatigue Life Prediction for Composite Panels

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Comparison of Elevated Temperature Tensile Properties and Fatigue Behavior of Two Variants of a Woven SiC/SiC Composite

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Brewer, David N.; Sreeramesh, Kalluri

2005-01-01

Tensile properties (elastic modulus, proportional limit strength, in-plane tensile strength, and strain at failure) of two variants of a woven SiC/SiC composite, manufactured during two separate time periods (9/99 and 1/01), were determined at 1038 and 1204 C by conducting tensile tests on specimens machined from plates. Continuous cycling fatigue tests (R = 0.05) and 20 cpm) were also conducted at the same two temperatures on specimens from both composites. In this study, average tensile properties, 95% confidence intervals associated with the tensile properties, and geometric mean fatigue lives of both composite materials are compared. The observed similarities and differences in the tensile properties are highlighted and an attempt is made to understand the relationship, if any, between the tensile properties and the fatigue behaviors of the two woven composites.

Active Video Game Playing in Children and Adolescents With Cystic Fibrosis: Exercise or Just Fun?

PubMed

Salonini, Elena; Gambazza, Simone; Meneghelli, Ilaria; Tridello, Gloria; Sanguanini, Milva; Cazzarolli, Clizia; Zanini, Alessandra; Assael, Baroukh M

2015-08-01

Xbox Kinect has been proposed as an exercise intervention in cystic fibrosis (CF), but its potential has not been compared with standard training modalities. Using a crossover design, subjects were randomized to 2 intervention groups: Xbox Kinect and a traditional stationary cycle. Heart rate, SpO2, dyspnea, and fatigue were measured. Subject satisfaction was tested. Thirty subjects with CF (11 males, mean ± SD age of 12 ± 2.5 y, mean ± SD FEV1 of 73 ± 16% of predicted) were enrolled. Xbox Kinect provided a cardiovascular demand similar to a stationary cycle, although the modality was different (interval vs. continuous). Maximum heart rates were similar (P = .2). Heart rate target was achieved more frequently with a stationary cycle (P = .02). Xbox Kinect caused less dyspnea (P = .001) and fatigue (P < .001) and was more enjoyable than a stationary cycle (P < .001). Subjects preferred Xbox Kinect for its interactivity. Xbox Kinect has the potential to be employed as an exercise intervention in young subjects with CF, but investigation over longer periods is needed. Copyright © 2015 by Daedalus Enterprises.

Multiple autoclave cycle effects on cyclic fatigue of nickel-titanium rotary files produced by new manufacturing methods.

PubMed

Hilfer, Paul B; Bergeron, Brian E; Mayerchak, Michael J; Roberts, Howard W; Jeansonne, Billie G

2011-01-01

Novel nickel-titanium rotary files with proprietary manufacturing techniques have recently been marketed. The purpose of this study was to assess multiple autoclave cycle effects on cyclic fatigue of GT Series X files (Dentsply Tulsa Dental Specialties, Tulsa, OK) and Twisted Files (SybronEndo, Orange, CA) METHODS: A jig using a 5-mm radius curve with 90° of maximum file flexure was used to induce cyclic fatigue failure. Files (n = 10) representing each experimental group (GT Series X 20/.04 and 20/.06; Twisted Files 25/.04 and 25/.06) were first tested to establish baseline mean cycles to failure (MCF). Experimental groups (n = 20) were then cycled to 25% of the established baseline MCF and then autoclaved. Additional autoclaving was accomplished at 50% and 75% of MCF followed by continual testing until failure. Control groups (n = 20) underwent the same procedures except autoclaving was not accomplished. The GT Series X (20/.04 and 20/.06) files showed no significant difference (p = 0.918/p = 0.096) in MCF for experimental versus control files. Twisted Files (25/.04) showed no significant difference (p = 0.432) in MCF between experimental and control groups. However, the Twisted Files (25/.06) experimental group showed a significantly lower (p = 0.0175) MCF compared with the controls. Under the conditions of this evaluation, autoclave sterilization significantly decreased cyclic fatigue resistance of one of the four file groups tested. Repeated autoclaving significantly reduced the MCF of 25/.06 Twisted Files; however, 25/.04 Twisted Files and both GT Series X files tested were not significantly affected by the same conditions. Published by Elsevier Inc.

Benchmark notch test for life prediction

NASA Technical Reports Server (NTRS)

Domas, P. A.; Sharpe, W. N.; Ward, M.; Yau, J. F.

1982-01-01

The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.

Damage accumulation in titanium matrix composites under generic hypersonic vehicle flight simulation and sustained loads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, W.S.; Mirdamadi, M.; Bakuckas, J.G. Jr.

1996-12-31

Titanium matrix composites (TMC), such as Ti-15V-3Cr-3Al-3Sn (Ti-15-3) reinforced with continuous silicon-carbide fibers (SCS-6), are being evaluated for use in hypersonic vehicles and advanced gas turbine engines where high strength-to-weight and high stiffness-to-weight ratios at elevated temperatures are critical. Such applications expose the composite to mechanical fatigue loading as well as thermally induced cycles. The damage accumulation behavior of a [0/90]2s laminate made of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a simulated generic hypersonic flight profile, portions of the flight profile, and sustained loads was evaluated experimentally. Portions of the flight profile were used separately tomore » isolate combinations of load and time at temperature that influenced the fatigue behavior of the composite. Sustained load tests were also conducted and the results were compared with the fatigue results under the flight profile and its portions. The test results indicated that the fatigue strength of this materials system is considerably reduced by a combination of load and time at temperature.« less

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

NASA Astrophysics Data System (ADS)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

An analysis of isothermal, bithermal, and thermomechanical fatigue data of Haynes 188 and B1900+Hf by energy considerations

NASA Technical Reports Server (NTRS)

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

1993-01-01

The low-cycle fatigue behavior of Haynes 188 and B1900+Hf under isothermal, bithermal, and thermomechanical loading conditions has been analyzed on the basis of the total hysteresis energy expended per cycle. It has been observed that in the case of isothermal fatigue the total hysteresis energy correlates well with the fatigue life. In the case of bithermal 'high rate' fatigue, for a given total hysteresis energy per cycle, the fatigue life is equal to or greater than the isothermal fatigue life at the maximum bithermal temperature. This observation could be used to establish a lower bound on life for design purposes. In one case of bithermal creep-fatigue and in thermomechanical fatigue, the life is shorter than that corresponding to the isothermal life at the maximum temperature. The energy supplied, per se, may not always give a systematic correlation with the fatigue life in the cases where time-dependent creep and environmental effects are encountered. Thus, in bithermal creep-fatigue and thermomechanical fatigue, the role of creep and environment and their dependence on the energy supplied have to be properly accounted for before the energy term can be used for life prediction.

Effects of temperature, thermal exposure, and fatigue on an alumina/aluminum composite

NASA Technical Reports Server (NTRS)

Olsen, G. C.

1980-01-01

An experimental investigation of the mechanical properties and microstructure of an aluminum matrix/polycrystalline alumina fiber composite material is discussed. The effects of fabrication, isothermal exposure (up to 10,000 hours at 590 K), thermal cycling (6000 cycles between 200 K and 590 K), fatigue (1,000,000 tension-tension cycles) were determined by mechanical testing and metallurgical analysis. The fabrication process severely degraded the fiber strength by reducing the alumina to a nonstoichiometric form and quenching in the resultant vacancies and stress fields. However, isothermal exposure, thermal cycling, and fatigue cycling all restored the fiber strength by enhancing vacancy annihilation. Comparison of the as-fabricated material with other aerospace materials shows that it is an attractive candidate for select applications. Long duration isothermal exposure weakened the matrix by overaging and through the diffusional loss of lithium to a surface reaction forming lithium carbonate. Thermal cycling initiated cracks in the matrix and fibers. Tension-tension fatigue cycling caused no apparent damage to the as-fabricated material but in fact, strengthened it to the rule-of-mixtures value. Fatigue cycling after thermal exposure did have a cumulative damage effect.

Spinal Cord Excitability and Sprint Performance Are Enhanced by Sensory Stimulation During Cycling

PubMed Central

Pearcey, Gregory E. P.; Noble, Steven A.; Munro, Bridget; Zehr, E. Paul

2017-01-01

Spinal cord excitability, as assessed by modulation of Hoffmann (H-) reflexes, is reduced with fatiguing isometric contractions. Furthermore, spinal cord excitability is reduced during non-fatiguing arm and leg cycling. Presynaptic inhibition of Ia terminals is believed to contribute to this suppression of spinal cord excitability. Electrical stimulation to cutaneous nerves reduces Ia presynaptic inhibition, which facilitates spinal cord excitability, and this facilitation is present during arm cycling. Although it has been suggested that reducing presynaptic inhibition may prolong fatiguing contractions, it is unknown whether sensory stimulation can alter the effects of fatiguing exercise on performance or spinal cord excitability. Thus, the aim of this experiment was to determine if sensory stimulation can interfere with fatigue-related suppression of spinal cord excitability, and alter fatigue rates during cycling sprints. Thirteen participants randomly performed three experimental sessions that included: unloaded cycling with sensory stimulation (CONTROL + STIM), sprints with sensory stimulation (SPRINT + STIM) and sprints without stimulation (SPRINT). Seven participants also performed a fourth session (CONTROL), which consisted of unloaded cycling. During SPRINT and SPRINT + STIM, participants performed seven, 10 s cycling sprints interleaved with 3 min rest. For CONTROL and CONTROL + STIM, participants performed unloaded cycling for ~30 min. During SPRINT + STIM and CONTROL + STIM, participants received patterned sensory stimulation to nerves of the right foot. H-reflexes and M-waves of the right soleus were evoked by stimulation of the tibial nerve at multiple time points throughout exercise. Sensory stimulation facilitated soleus H-reflexes during unloaded cycling, whereas sprints suppressed soleus H-reflexes. While receiving sensory stimulation, there was less suppression of soleus H-reflexes and slowed reduction in average power output, compared to sprints without stimulation. These results demonstrate that sensory stimulation can substantially mitigate the fatiguing effects of sprints. PMID:29326570

Spinal Cord Excitability and Sprint Performance Are Enhanced by Sensory Stimulation During Cycling.

PubMed

Pearcey, Gregory E P; Noble, Steven A; Munro, Bridget; Zehr, E Paul

2017-01-01

Spinal cord excitability, as assessed by modulation of Hoffmann (H-) reflexes, is reduced with fatiguing isometric contractions. Furthermore, spinal cord excitability is reduced during non-fatiguing arm and leg cycling. Presynaptic inhibition of Ia terminals is believed to contribute to this suppression of spinal cord excitability. Electrical stimulation to cutaneous nerves reduces Ia presynaptic inhibition, which facilitates spinal cord excitability, and this facilitation is present during arm cycling. Although it has been suggested that reducing presynaptic inhibition may prolong fatiguing contractions, it is unknown whether sensory stimulation can alter the effects of fatiguing exercise on performance or spinal cord excitability. Thus, the aim of this experiment was to determine if sensory stimulation can interfere with fatigue-related suppression of spinal cord excitability, and alter fatigue rates during cycling sprints. Thirteen participants randomly performed three experimental sessions that included: unloaded cycling with sensory stimulation ( CONTROL + STIM ), sprints with sensory stimulation ( SPRINT + STIM ) and sprints without stimulation ( SPRINT ). Seven participants also performed a fourth session ( CONTROL ), which consisted of unloaded cycling. During SPRINT and SPRINT + STIM, participants performed seven, 10 s cycling sprints interleaved with 3 min rest. For CONTROL and CONTROL + STIM , participants performed unloaded cycling for ~30 min. During SPRINT + STIM and CONTROL + STIM , participants received patterned sensory stimulation to nerves of the right foot. H-reflexes and M-waves of the right soleus were evoked by stimulation of the tibial nerve at multiple time points throughout exercise. Sensory stimulation facilitated soleus H-reflexes during unloaded cycling, whereas sprints suppressed soleus H-reflexes. While receiving sensory stimulation, there was less suppression of soleus H-reflexes and slowed reduction in average power output, compared to sprints without stimulation. These results demonstrate that sensory stimulation can substantially mitigate the fatiguing effects of sprints.

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

NASA Technical Reports Server (NTRS)

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

2000-01-01

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

Ultrahigh vacuum, high temperature, low cycle fatigue of coated and uncoated Rene 80

NASA Technical Reports Server (NTRS)

Kortovich, C. S.

1976-01-01

A study was conducted on the ultrahigh vacuum strain controlled by low cycle fatigue behavior of uncoated and CODEP B-1 aluminide coated Rene' 80 nickel-base superalloy at 1000 C (1832 F) and 871 C (1600 F). The results indicated little effect of coating or temperature on the fatigue properties. There was, however, a significant effect on fatigue life when creep was introduced into the strain cycles. The effect of this creep component was analyzed in terms of the method of strainrange partitioning.

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

NASA Technical Reports Server (NTRS)

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.

Problems of the high-cycle fatigue of the materials intended for the parts of modern gas-turbine engines and power plants

NASA Astrophysics Data System (ADS)

Petukhov, A. N.

2010-10-01

The problems related to the determination of the life of the structural materials applied for important parts in gas-turbine engines and power plants from the results of high-cycle fatigue tests are discussed. Methods for increasing the reliability of the high-cycle fatigue characteristics and the factors affecting the operational reliability are considered.

The time of day differently influences fatigue and locomotor activity: is body temperature a key factor?

PubMed

Machado, Frederico Sander Mansur; Rodovalho, Gisele Vieira; Coimbra, Cândido Celso

2015-03-01

The aim of this study was to verify the possible interactions between exercise capacity and spontaneous locomotor activity (SLA) during the oscillation of core body temperature (Tb) that occurs during the light/dark cycle. Wistar rats (n=11) were kept at an animal facility under a light/dark cycle of 14/10h at an ambient temperature of 23°C and water and food ad libitum. Initially, in order to characterize the daily oscillation in SLA and Tb of the rats, these parameters were continuously recorded for 24h using an implantable telemetric sensor (G2 E-Mitter). The animals were randomly assigned to two progressive exercise test protocols until fatigue during the beginning of light and dark-phases. Fatigue was defined as the moment rats could not keep pace with the treadmill. We assessed the time to fatigue, workload and Tb changes induced by exercise. Each test was separated by 3days. Our results showed that exercise capacity and heat storage were higher during the light-phase (p<0.05). In contrast, we observed that both SLA and Tb were higher during the dark-phase (p<0.01). Notably, the correlation analysis between the amount of SLA and the running capacity observed at each phase of the daily cycle revealed that, regardless of the time of the day, both types of locomotor physical activity have an important inherent component (r=0.864 and r=0.784, respectively, p<0.01) without a direct relationship between them. This finding provides further support for the existence of specific control mechanisms for each type of physical activity. In conclusion, our data indicate that the relationship between the body temperature and different types of physical activity might be affected by the light/dark cycle. These results mean that, although exercise performance and spontaneous locomotor activity are not directly associated, both are strongly influenced by daily cycles of light and dark. Copyright © 2014 Elsevier Inc. All rights reserved.

Electrically induced contraction levels of the quadriceps femoris muscles in healthy men: the effects of three patterns of burst-modulated alternating current and volitional muscle fatigue.

PubMed

Parker, Michael G; Broughton, Alex J; Larsen, Ben R; Dinius, Josh W; Cimbura, Mac J; Davis, Matthew

2011-12-01

The purpose of this study was to compare electrically induced contraction levels produced by three patterns of alternating current in fatigued and nonfatigued skeletal muscles. Eighteen male volunteers without health conditions, with a mean (SD) age of 24.9 (3.4) yrs were randomly exposed to a fatiguing volitional isometric quadriceps contraction and one of three patterns of 2.5-KHz alternating current; two were modulated at 50 bursts per second (10% burst duty cycle with five cycles per burst and 90% burst duty cycle with 45 cycles per burst), and one pattern was modulated at 100 bursts per second (10% burst duty cycle with 2.5 cycles per burst). The electrically induced contraction levels produced by the three patterns of electrical stimulation were compared before and after the fatiguing contraction. The 10% burst duty cycles produced 42.9% (95% confidence interval, 29.1%-56.7%) and 32.1% (95% confidence interval, 18.2%-45.9%) more muscle force (P < 0.001) than did the 90% burst duty cycle pattern. There was no significant interaction effect (P = 0.392) of electrical stimulation patterns and fatigue on the electrically induced contraction levels. The lower burst duty cycle (10%) patterns of electrical stimulation produced stronger muscle contractions. Furthermore, the stimulation patterns had no influence on the difference in muscle force before and after the fatiguing quadriceps contraction. Consequently, for clinical applications in which high forces are desired, the patterns using the 10% burst duty cycle may be helpful.

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

Acoustic emission characteristics of copper alloys under low-cycle fatigue conditions

NASA Technical Reports Server (NTRS)

Krampfner, Y.; Kawamoto, A.; Ono, K.; Green, A.

1975-01-01

The acoustic emission (AE) characteristics of pure copper, zirconium-copper, and several copper alloys were determined to develop nondestructive evaluation schemes of thrust chambers through AE techniques. The AE counts rms voltages, frequency spectrum, and amplitude distribution analysis evaluated AE behavior under fatigue loading conditions. The results were interpreted with the evaluation of wave forms, crack propagation characteristics, as well as scanning electron fractographs of fatigue-tested samples. AE signals at the beginning of a fatigue test were produced by a sample of annealed alloys. A sample of zirconium-containing alloys annealed repeatedly after each fatigue loading cycle showed numerous surface cracks during the subsequent fatigue cycle, emitting strong-burst AE signals. Amplitude distribution analysis exhibits responses that are characteristic of certain types of AE signals.

Resistance Spot Welding Characteristics and High Cycle Fatigue Behavior of DP 780 Steel Sheet

NASA Astrophysics Data System (ADS)

Pal, Tapan Kumar; Bhowmick, Kaushik

2012-02-01

Resistance spot welding characteristics of DP 780 steel was investigated using peel test, microhardness test, tensile shear test, and fatigue test. Tensile shear test provides better spot weld quality than conventional peel test and hardness is not a good indicator of the susceptibility to interfacial fracture. The results of high-cycle fatigue behavior of spot welded DP 780 steel under two different parameters show that at high load low cycle range a significant difference in the S- N curve and almost similar fatigue behavior of spot welds at low load high cycle range are obtained. However, when applied load was converted to stress intensity factor, the difference in the fatigue behavior between welds diminished. Furthermore, a transition in fracture mode, i.e., interfacial and plug and hole-type at about 50% of yield load is observed.

Fatigue damage assessment of high-usage in-service aircraft fuselage structure

NASA Astrophysics Data System (ADS)

Mosinyi, Bao Rasebolai

As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a fatigue lead crack of critical length. The presence of MSD also reduces the structure's ability to withstand longer cracks. The objective of the current study is to assess, both experimentally and analytically, MSD formation and growth in the lap joint of curved panels removed from a retired aircraft. A Boeing 727-232 airplane owned and operated by Delta Air Lines, and retired at its design service goal, was selected for the study. Two panels removed from the left-hand side of the fuselage crown, near stringer 4L, were subjected to extended fatigue testing using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration (FAA) William J. Hughes Technical Center. The state of MSD was continuously assessed using several nondestructive inspection (NDI) methods. Damage to the load attachment points of the first panel resulted in termination of the fatigue test at 43,500 fatigue cycles, before cracks had developed in the lap joint. The fatigue test for the second panel was initially conducted under simulated in-service loading conditions for 120,000 cycles, and no cracks were detected in the skin of the panel test section. Artificial damage was then introduced into the panel at selected rivets in the critical (lower) rivet row, and the fatigue loads were increased. Visually detectable crack growth from the artificial notches was first seen after 133,000 cycles. The resulting lead crack grew along the lower rivet row, eventually forming an 11.8" long unstable crack after 141,771 cycles, at which point the test was terminated. Posttest fractograpic examinations of the crack surfaces were conducted, revealing the presence of subsurface MSD at the critical rivet row of the lap joint. Special attention was also given to the stringer clips that attach the fuselage frames to the stringers, since they also experienced cracking during the fatigue tests. The performance of the different conventional and emerging NDI methods was also assessed, and some of the emerging NDI methods were quite effective in detecting and measuring the length of subsurface cracks. Delta Air Lines conducted a separate destructive investigation on the state of damage along the right-hand side of the fuselage, near stringer 4R. A comparison of these two studies showed that the lap joint on the left hand-side of the aircraft, along stringer 4L, had better fatigue life than the one on the opposite side, along stringer 4R. The cause of the difference in fatigue life was investigated by close examination of the rivet installation qualities, and was found to be a result of better rivet installation along the lap joint at stringer 4L. Finite element models for both the skin and substructures of the panels were developed and geometrically nonlinear finite element analyses were conducted to verify the loading conditions and to determine near-field parameters governing MSD initiation and growth. Fatigue crack growth predictions based on the NASGRO equation were in good agreement with the experimental crack growth data for through-the-thickness cracks. For subsurface cracks, simulation of crack growth was found to correlate better with fractography data when an empirical crack growth model was used. The results of the study contribute to the understanding of the initiation and growth of MSD in the inner skin layer of a lap joint, and provide valuable data for the evaluation and validation of analytical methodologies to predict MSD initiation and growth and a better understanding on the effect of manufacturing quality on damage accumulation along the lap joint.

Cyclic fatigue analysis of rocket thrust chambers. Volume 1: OFHC copper chamber low cycle fatigue

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elasto-plastic strain analysis was performed for the throat section of a regeneratively cooled rocket combustion chamber. The analysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the chamber operating cycle. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen combustion chamber which was fatigue tested to failure. The computed strain range at typical chamber operating conditions was used in conjunction with oxygen-free, high-conductivity (OHFC) copper isothermal fatigue test data to predict chamber low-cycle fatigue life.

Fatigue damage mechanisms in boron-aluminium composite laminates

NASA Technical Reports Server (NTRS)

Dvorak, G. J.; Johnson, W. S.

1980-01-01

The relationship between fatigue and shakedown in metal matrix composites is investigated theoretically and experimentally for unidirectional and laminated 6061 Al-B materials. It is shown that no fatigue damage takes place if the applied stress range is such that the material remains elastic, or shakes down, i.e., resumes elastic cyclic straining after a small number of plastic strain cycles. Fatigue damage occurs only in specimens subjected to stress ranges which cause sustained cyclic plastic straining in the aluminum matrix. If the applied stress range is smaller than that required for fatigue failure, after about 10 to the 6th cycles a saturation damage state is reached which remains essentially unchanged with increasing number of cycles.

The application of probabilistic design theory to high temperature low cycle fatigue

NASA Technical Reports Server (NTRS)

Wirsching, P. H.

1981-01-01

Metal fatigue under stress and thermal cycling is a principal mode of failure in gas turbine engine hot section components such as turbine blades and disks and combustor liners. Designing for fatigue is subject to considerable uncertainty, e.g., scatter in cycles to failure, available fatigue test data and operating environment data, uncertainties in the models used to predict stresses, etc. Methods of analyzing fatigue test data for probabilistic design purposes are summarized. The general strain life as well as homo- and hetero-scedastic models are considered. Modern probabilistic design theory is reviewed and examples are presented which illustrate application to reliability analysis of gas turbine engine components.

Fatigue and failure responses of lead zirconate titanate multilayer actuator under unipolar high-field electric cycling

NASA Astrophysics Data System (ADS)

Zeng, Fan Wen; Wang, Hong; Lin, Hua-Tay

2013-07-01

Lead zirconate titanate (PZT) multilayer actuators with an interdigital electrode design were studied under high electric fields (3 and 6 kV/mm) in a unipolar cycling mode. A 100 Hz sine wave was used in cycling. Five specimens tested under 6 kV/mm failed from 3.8 × 105 to 7 × 105 cycles, whereas three other specimens tested under 3 kV/mm were found to be still functional after 108 cycles. Variations in piezoelectric and dielectric responses of the tested specimens were observed during the fatigue test, depending on the measuring and cycling conditions. Selected fatigued and damaged actuators were characterized using an impedance analyzer or small signal measurement. Furthermore, involved fatigue and failure mechanisms were investigated using scanning acoustic microscope and scanning electron microscope. The extensive cracks and porous regions were revealed across the PZT layers on the cross sections of a failed actuator. The results from this study have demonstrated that the high-field cycling can accelerate the fatigue of PZT stacks as long as the partial discharge is controlled. The small signal measurement can also be integrated into the large signal measurement to characterize the fatigue response of PZT stacks in a more comprehensive basis. The former can further serve as an experimental method to test and monitor the behavior of PZT stacks.

A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades

PubMed Central

Yue, Peng; Yu, Zheng-Yong; Wang, Qingyuan

2017-01-01

Combined high and low cycle fatigue (CCF) generally induces the failure of aircraft gas turbine attachments. Based on the aero-engine load spectrum, accurate assessment of fatigue damage due to the interaction of high cycle fatigue (HCF) resulting from high frequency vibrations and low cycle fatigue (LCF) from ground-air-ground engine cycles is of critical importance for ensuring structural integrity of engine components, like turbine blades. In this paper, the influence of combined damage accumulation on the expected CCF life are investigated for turbine blades. The CCF behavior of a turbine blade is usually studied by testing with four load-controlled parameters, including high cycle stress amplitude and frequency, and low cycle stress amplitude and frequency. According to this, a new damage accumulation model is proposed based on Miner’s rule to consider the coupled damage due to HCF-LCF interaction by introducing the four load parameters. Five experimental datasets of turbine blade alloys and turbine blades were introduced for model validation and comparison between the proposed Miner, Manson-Halford, and Trufyakov-Kovalchuk models. Results show that the proposed model provides more accurate predictions than others with lower mean and standard deviation values of model prediction errors. PMID:28773064

A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades.

PubMed

Zhu, Shun-Peng; Yue, Peng; Yu, Zheng-Yong; Wang, Qingyuan

2017-06-26

Combined high and low cycle fatigue (CCF) generally induces the failure of aircraft gas turbine attachments. Based on the aero-engine load spectrum, accurate assessment of fatigue damage due to the interaction of high cycle fatigue (HCF) resulting from high frequency vibrations and low cycle fatigue (LCF) from ground-air-ground engine cycles is of critical importance for ensuring structural integrity of engine components, like turbine blades. In this paper, the influence of combined damage accumulation on the expected CCF life are investigated for turbine blades. The CCF behavior of a turbine blade is usually studied by testing with four load-controlled parameters, including high cycle stress amplitude and frequency, and low cycle stress amplitude and frequency. According to this, a new damage accumulation model is proposed based on Miner's rule to consider the coupled damage due to HCF-LCF interaction by introducing the four load parameters. Five experimental datasets of turbine blade alloys and turbine blades were introduced for model validation and comparison between the proposed Miner, Manson-Halford, and Trufyakov-Kovalchuk models. Results show that the proposed model provides more accurate predictions than others with lower mean and standard deviation values of model prediction errors.

Creep and Fatigue Interaction in the PWA 1484 Single Crystal Nickel-Base Alloy (Preprint)

DTIC Science & Technology

2011-07-01

work by Zhang et al . has shown that during the early part of fatigue cycling dislocations are formed primarily in the γ matrix with the number of...dislocations increasing with the number of applied cycles [11]. Ott and Mughrabi showed that during fatigue of single crystal nickel base superalloys... al . and their research determined that the fatigue behavior of PWA1484 could be well represented by a Walker type fatigue model that also included

Fractographic evaluation of creep effects on strain-controlled fatigue-cracking of AISI 304LC and 316 stainless steel

NASA Technical Reports Server (NTRS)

Oldrieve, R. E.

1978-01-01

Analysis of high temperature low cycle fatigue of AISI 304LC and 316 stainless steels by the method of strainrange partitioning results in four separate strainrange versus life relationships, depending upon the way in which creep-strain and plastic strain are combined within a cycle. Fractography is used in this investigation of the creep-fatigue interaction associated with these cycles. The PP and PC-cycle fractures were transgranular. The PC-cycle resulted in fewer cycles of initiation and shorter total cyclic life for the same applied inelastic strainrange. The CC-cycle had mixed transgranular and intergranular fracture, fewer cycles of initiation and shorter cycle life than PP or PC. The CP-cycle had fully integranular cracking, and failed in fewer cycles than were required for cracks to initate for PP,PC, and CC.

Low-cycle fatigue analysis of a cooled copper combustion chamber

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elastoplastic strain analysis was performed for the throat section of regeneratively cooled rocket engine combustion chamber. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the engine operating cycle. The strain range was used in conjunction with OFHC copper isothermal fatigue test data to predict engine low-cycle fatigue life. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen chamber which was fatigue tested to failure at the NASA Lewis Research Center.

A Simulation of Low and High Cycle Fatigue Failure Effects for Metal Matrix Composites Based on Innovative J2-Flow Elastoplasticity Model

PubMed Central

Wang, Zhaoling; Xiao, Heng

2017-01-01

New elastoplastic J2-flow constitutive equations at finite deformations are proposed for the purpose of simulating the fatigue failure behavior for metal matrix composites. A new, direct approach is established in a two-fold sense of unification. Namely, both low and high cycle fatigue failure effects of metal matrix composites may be simultaneously simulated for various cases of the weight percentage of reinforcing particles. Novel results are presented in four respects. First, both the yield condition and the loading–unloading conditions in a usual sense need not be involved but may be automatically incorporated into inherent features of the proposed constitutive equations; second, low-to-high cycle fatigue failure effects may be directly represented by a simple condition for asymptotic loss of the material strength, without involving any additional damage-like variables; third, both high and low cycle fatigue failure effects need not be separately treated but may be automatically derived as model predictions with a unified criterion for critical failure states, without assuming any ad hoc failure criteria; and, finally, explicit expressions for each incorporated model parameter changing with the weight percentage of reinforcing particles may be obtainable directly from appropriate test data. Numerical examples are presented for medium-to-high cycle fatigue failure effects and for complicated duplex effects from low to high cycle fatigue failure effects. Simulation results are in good agreement with experimental data. PMID:28946637

Leg joint power output during progressive resistance FES-LCE cycling in SCI subjects: developing an index of fatigue.

PubMed

Haapala, Stephenie A; Faghri, Pouran D; Adams, Douglas J

2008-04-26

The purpose of this study was to investigate the biomechanics of the hip, knee and ankle during a progressive resistance cycling protocol in an effort to detect and measure the presence of muscle fatigue. It was hypothesized that knee power output can be used as an indicator of fatigue in order to assess the cycling performance of SCI subjects. Six spinal cord injured subjects (2 incomplete, 4 complete) between the ages of twenty and fifty years old and possessing either a complete or incomplete spinal cord injury at or below the fourth cervical vertebra participated in this study. Kinematic data and pedal forces were recorded during cycling at increasing levels of resistance. Ankle, knee and hip power outputs and resultant pedal force were calculated. Ergometer cadence and muscle stimulation intensity were also recorded. The main findings of this study were: (a) ankle and knee power outputs decreased, whereas hip power output increased with increasing resistance, (b) cadence, stimulation intensity and resultant pedal force in that combined order were significant predictors of knee power output and (c) knowing the value of these combined predictors at 10 rpm, an index of fatigue can be developed, quantitatively expressing the power capacity of the knee joint with respect to a baseline power level defined as fatigue. An index of fatigue was successfully developed, proportionalizing knee power capacity during cycling to a predetermined value of fatigue. The fatigue index value at 0/8th kp, measured 90 seconds into active, unassisted pedaling was 1.6. This indicates initial power capacity at the knee to be 1.6 times greater than fatigue. The fatigue index decreased to 1.1 at 2/8th kp, representing approximately a 30% decrease in the knee's power capacity within a 4 minute timespan. These findings suggest that the present cycling protocol is not sufficient for a rider to gain the benefits of FES and thus raises speculation as to whether or not progressive resistance cycling is an appropriate protocol for SCI subjects.

Leg joint power output during progressive resistance FES-LCE cycling in SCI subjects: developing an index of fatigue

PubMed Central

Haapala, Stephenie A; Faghri, Pouran D; Adams, Douglas J

2008-01-01

Background The purpose of this study was to investigate the biomechanics of the hip, knee and ankle during a progressive resistance cycling protocol in an effort to detect and measure the presence of muscle fatigue. It was hypothesized that knee power output can be used as an indicator of fatigue in order to assess the cycling performance of SCI subjects. Methods Six spinal cord injured subjects (2 incomplete, 4 complete) between the ages of twenty and fifty years old and possessing either a complete or incomplete spinal cord injury at or below the fourth cervical vertebra participated in this study. Kinematic data and pedal forces were recorded during cycling at increasing levels of resistance. Ankle, knee and hip power outputs and resultant pedal force were calculated. Ergometer cadence and muscle stimulation intensity were also recorded. Results The main findings of this study were: (a) ankle and knee power outputs decreased, whereas hip power output increased with increasing resistance, (b) cadence, stimulation intensity and resultant pedal force in that combined order were significant predictors of knee power output and (c) knowing the value of these combined predictors at 10 rpm, an index of fatigue can be developed, quantitatively expressing the power capacity of the knee joint with respect to a baseline power level defined as fatigue. Conclusion An index of fatigue was successfully developed, proportionalizing knee power capacity during cycling to a predetermined value of fatigue. The fatigue index value at 0/8th kp, measured 90 seconds into active, unassisted pedaling was 1.6. This indicates initial power capacity at the knee to be 1.6 times greater than fatigue. The fatigue index decreased to 1.1 at 2/8th kp, representing approximately a 30% decrease in the knee's power capacity within a 4 minute timespan. These findings suggest that the present cycling protocol is not sufficient for a rider to gain the benefits of FES and thus raises speculation as to whether or not progressive resistance cycling is an appropriate protocol for SCI subjects. PMID:18439300

The Longitudinal Relationship between Fatigue and Sleep in Breast Cancer Patients Undergoing Chemotherapy

PubMed Central

Liu, Lianqi; Rissling, Michelle; Natarajan, Loki; Fiorentino, Lavinia; Mills, Paul J.; Dimsdale, Joel E.; Sadler, Georgia Robins; Parker, Barbara A.; Ancoli-Israel, Sonia

2012-01-01

Study Objective: Fatigue and sleep disturbances are two of the most common and distressing symptoms of cancer patients. A relationship between the two symptoms was reported in symptom cluster studies; however, only subjective measurements of sleep were examined and most studies were cross-sectional. In this study of women with breast cancer undergoing chemotherapy, we explored the longitudinal relationship between fatigue and sleep measured both subjectively and objectively. Design: Prospective study. Data were collected at 7 time points: before (baseline) and during the 3 weeks of cycle 1 and cycle 4 chemotherapy. Participants: Ninety-seven women with newly diagnosed stage I-III breast cancer who were scheduled to receive at least four 3-week cycles of chemotherapy. Measurement and Results: Objective sleep parameters were measured with an Actillume actigraph (Ambulatory Monitoring Inc.). Subjective sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). Fatigue was assessed with the Multidimensional Fatigue Symptom Inventory-Short Form (MFSI-SF). Fatigue became worse during both cycles of chemotherapy (P-values < 0.01). Subjective sleep quality was poor at baseline and remained unchanged throughout treatment. Objective nighttime and daytime total sleep time increased compared to baseline during the treatment administration week of both cycles; daytime total wake time decreased during the treatment week of both cycles and during the last 2 week of cycle 4. Mixed model results revealed that fatigue was positively associated with total PSQI scores and with objective measures of total nap time, and negatively associated with total wake time during the day (all P-values < 0.01). Conclusion: Fatigue was significantly associated with subjective reports of poor sleep and objective measures of daytime sleepiness, but not with nocturnal sleep as measured with actigraphy. This relationship between fatigue and sleep warrants further studies to explore their possible common underlying etiology. Citation: Liu L; Rissling M; Natarajan L; Fiorentino L; Mills PJ; Dimsdale JE; Sadler GR; Parker BA; Ancoli-Israel S. The longitudinal relationship between fatigue and sleep in breast cancer patients undergoing chemotherapy. SLEEP 2012;35(2):237-245. PMID:22294814

Microstructure-Sensitive Extreme Value Probabilities for High Cycle Fatigue of Ni-Base Superalloy IN100 (Preprint)

DTIC Science & Technology

2009-03-01

transition fatigue regimes; however, microplasticity (i.e., heterogeneous plasticity at the scale of microstructure) is relevant to understanding fatigue...and Socie [57] considered the affect of microplastic 14 Microstructure-Sensitive Extreme Value Probabilities for High Cycle Fatigue of Ni-Base...considers the local stress state as affected by intergranular interactions and microplasticity . For the calculations given below, the volumes over which

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

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

NASA Astrophysics Data System (ADS)

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

2000-05-01

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

The Effects of Hot Corrosion Pits on the Fatigue Resistance of a Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Telesman, Jack; Hazel, Brian; Mourer, David P.

2009-01-01

The effects of hot corrosion pits on low cycle fatigue life and failure modes of the disk superalloy ME3 were investigated. Low cycle fatigue specimens were subjected to hot corrosion exposures producing pits, then tested at low and high temperatures. Fatigue lives and failure initiation points were compared to those of specimens without corrosion pits. Several tests were interrupted to estimate the fraction of fatigue life that fatigue cracks initiated at pits. Corrosion pits significantly reduced fatigue life by 60 to 98 percent. Fatigue cracks initiated at a very small fraction of life for high temperature tests, but initiated at higher fractions in tests at low temperature. Critical pit sizes required to promote fatigue cracking were estimated, based on measurements of pits initiating cracks on fracture surfaces.

An Investigation on the Wear Resistance and Fatigue Behaviour of Ti-6Al-4V Notched Members Coated with Hydroxyapatite Coatings

PubMed Central

Oskouei, Reza H; Fallahnezhad, Khosro; Kuppusami, Sushmitha

2016-01-01

In this study, surface properties of Ti-6Al-4V alloy coated with hydroxyapatite coatings were investigated. Wear resistance and fatigue behaviour of samples with coating thicknesses of 10 and 50 µm as well as uncoated samples were examined. Wear experiments demonstrated that the friction factor of the uncoated titanium decreased from 0.31 to 0.06, through a fluctuating trend, after 50 cycles of wear tests. However, the friction factor of both the coated samples (10 and 50 µm) gradually decreased from 0.20 to 0.12 after 50 cycles. At the end of the 50th cycle, the penetration depth of the 10 and 50 µm coated samples were 7.69 and 6.06 µm, respectively. Fatigue tests showed that hydroxyapatite coatings could improve fatigue life of a notched Ti-6Al-4V member in both low and high cycle fatigue zones. It was understood, from fractography of the fracture surfaces, that the fatigue zone of the uncoated specimens was generally smaller in comparison with that of the coated specimens. No significant difference was observed between the fatigue life of coated specimens with 10 and 50 µm thicknesses. PMID:28787911

Environmental Effects on Graphite-Epoxy Fatigue Properties

NASA Technical Reports Server (NTRS)

Sumsion, H. T.

1976-01-01

Effects of torsional and flexural fatigue on the long-time Integrity of advanced graphite-epoxy structural composites have been investigated. Torsional fatigue tests were run at stress ratios of R = 0 (zero to maximum, repeated) and R = -1 (zero mean stress) on unidirectional, angleply, and woven graphite fiber materials in air and water at room temperature and at 74 C. Flexural fatigue tests (four-point bending) with R = -1 were run in air and water at room temperature, and with R = 0 in air. Results show that, in torsional cycling, both water environment and higher test temperature contribute to significant degradation of torsional stiffness. The degradation of stiffness from torsional stress cycling was observed to be much greater with R = -1 than with simple R = 0 cycling. The effect of environment also is greater in the fully reversed cycling. Flexural fatigue results on +/- 30 deg material show a large fatigue effect, with fatigue limits of less than 50% and 30% of the static failure strength for specimens tested under stress ratios of R = 0 and R = -1, respectively. Compliance measurements indicate that the final failures are preceded by damage initiation and accumulation, which begins at about 1% of the specimen life.

Microstructural modeling of fatigue fracture of shape memory alloys at thermomechanical cyclic loading

NASA Astrophysics Data System (ADS)

Belyaev, Fedor S.; Evard, Margarita E.; Volkov, Aleksandr E.

2018-05-01

A microstructural model of shape memory alloys (SMA) describing their deformation and fatigue fracture is presented. A new criterion of fracture has been developed which takes into account the effect of hydrostatic pressure, deformation defects and material damage. It is shown that the model can describe the fatigue fracture of SMA under various thermomechanical cycling regimes. Results of calculating the number of cycles to failure at thermocycling under a constant stress, at symmetric two-sided cyclic deformation, at straining-unloading cycles, at cycling in the regime of the thermodynamic cycles of a SMA working body in the hard (strain controlled) and soft (stress controlled) working cycles, is studied. Results of calculating the number of cycles to failure are presented for different parameters of these cycles.

Thermal-Fatigue Crack-Growth Characteristics and Mechanical Strain Cycling Behavior of A-286 Discaloy, and 16-25-6 Austenitic Steels

NASA Technical Reports Server (NTRS)

Smith, Robert W.; Smith, Gordon T.

1960-01-01

Thermal-fatigue crack-growth characteristics of notched- and unnotched-disk specimens of A-286, Discaloy, hot-cold worked 16-25-6, and overaged 16-25-6 were experimentally studied. Separately controlled variables were total strain range (0.0043 to 0.0079 in./in.), maximum cycle temperature (1300 and 1100 F), and hold time at maximum temperature (O and 5 min). A limited number of mechanical, push-pull, constant-strain cycle tests at room temperature were made using notched and un-notched bars of the same materials. In these tests the number of cycles to failure as well as the variation of load change with accumulated cycles was measured, and the effects of mean stress were observed. Constant-strain-range mechanical-fatigue tests at room temperature revealed notched-bar fatigue life to be strongly influenced by mean stress. For a specific strain range, the longest fatigue life was always found to be associated with the least-tensile (or most compressive) mean stress. By defining thermal-fatigue life as the number of cycles required to produce a crack area of 6000 square mils, the relative thermal-fatigue resistances of the test materials were established. Notched-disk specimens of A-286 and Discaloy steels exhibited longer fatigue lives than either hot-cold worked or overaged 16-25-6. On the other hand, unnotched-disk specimens of Discaloy and hot-cold worked 16-25-6 had longer lives than A-286 and overaged 16-25-6. Separation of the crack-growth data into microstage and macrostage periods revealed that the macrostage period accounted for the greatest part of the difference among materials when tested in the notched configuration, while the microstage was largely responsible for the differences encountered in unnotched disks.

Bithermal Low-Cycle Fatigue Evaluation of Automotive Exhaust System Alloy SS409

NASA Technical Reports Server (NTRS)

Lu, Gui-Ying; Behling, Mike B.; Halford, Gary R.

2000-01-01

This investigation provides, for the first time, cyclic strainrange-controlled, thermomechanical fatigue results for the ferritic stainless steel alloy SS409. The alloy has seen extensive application for automotive exhaust system components. The data were generated to calibrate the Total Strain Version of the Strainrange Partitioning (TS-SRP) method for eventual application to the design and durability assessment of automotive exhaust systems. The thermomechanical cyclic lifetime and cyclic stress-strain constitutive behavior for alloy SS409 were measured using bithermal tests cycling between isothermal extremes of 400 and 800 C. Lives ranged up to 10,000 cycles to failure with hold-times of 0.33 to 2.0 minutes. The bithermal fatigue behavior is compared to isothermal, strain-controlled fatigue behavior at both 400 and 800 C. Thermomechanical cycling was found to have a profound detrimental influence on the fatigue failure resistance of SS409 compared to isothermal cycling. Supplementary bithermal cyclic stress-strain constitutive tests with hold-times ranging from 40 seconds up to 1.5 hours were conducted to calibrate the TS-SRP equation for extrapolation to longer lifetime predictions. Observed thermomechanical (bithermal) fatigue lives correlated well with lives calculated using the calibrated TS-SRP equations: 70% of the bithermal fatigue data fall within a factor of 1.2 of calculated life; 85% within a factor of 1.4; and 100% within a factor of 1.8.

The 6-min mastication test: a unique test to assess endurance of continuous chewing, normal values, reliability, reproducibility and usability in patients with mitochondrial disease.

PubMed

van den Engel-Hoek, L; Knuijt, S; van Gerven, M H J C; Lagarde, M L J; Groothuis, J T; de Groot, I J M; Janssen, M C H

2017-03-01

In patients with mitochondrial disease, fatigue and muscle problems are the most common complaints. They also experience these complaints during mastication. To measure endurance of continuous mastication in patients with mitochondrial diseases, the 6-min mastication test (6MMT) was developed. This study included the collection of normal data for the 6MMT in a healthy population (children and adults). During 6 min of continuous mastication on a chew tube chewing cycles per minute, total amount of chewing cycles and the difference between minute 1 (M 1 ) and minute 6 (M 2 ) were collected in 271 healthy participants (5-80 years old). These results were compared with those of nine paediatric and 25 adult patients with a mitochondrial disease. Visual analogue scale (VAS) scores were collected directly after the test and after 5 min. A qualitative rating was made on masticatory movements. The reproducibility of the 6MMT in the healthy population with an interval of approximately 2 weeks was good. The inter-rater reliability for the observations was excellent. The patient group demonstrated lower total amount of chewing cycles or had greater differences between M 1 and M 6 . The 6MMT is a reliable and objective test to assess endurance of continuous chewing. It demonstrates the ability of healthy children and adults to chew during 6 min with a highly stable frequency of mastication movements. The test may give an explanation for the masticatory problems in patient groups, who are complaining of pain and fatigue during mastication. © 2017 John Wiley & Sons Ltd.

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

NASA Technical Reports Server (NTRS)

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

2002-01-01

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

Exploratory Development of Improved Fatigue Strength Adhesives

DTIC Science & Technology

1974-11-01

fiber reinforced adhesives. A fifty-fold in-j crease in fatigue life at equivalent stress levels was achieved when a woven high modulus graphite...the stress level which could survive 10’ fatigue cycles was increased from approximately 30 percent of the ultimate shear strength with nylor knit...supports to as much as fifty percent with the high modulus fiber bond line reinforcement. The stress level which could withstand 10’ fatigue cycles

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

NASA Astrophysics Data System (ADS)

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

2001-09-01

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

Polarization fatigue of organic ferroelectric capacitors

PubMed Central

Zhao, Dong; Katsouras, Ilias; Li, Mengyuan; Asadi, Kamal; Tsurumi, Junto; Glasser, Gunnar; Takeya, Jun; Blom, Paul W. M.; de Leeuw, Dago M.

2014-01-01

The polarization of the ferroelectric polymer P(VDF-TrFE) decreases upon prolonged cycling. Understanding of this fatigue behavior is of great technological importance for the implementation of P(VDF-TrFE) in random-access memories. However, the origin of fatigue is still ambiguous. Here we investigate fatigue in thin-film capacitors by systematically varying the frequency and amplitude of the driving waveform. We show that the fatigue is due to delamination of the top electrode. The origin is accumulation of gases, expelled from the capacitor, under the impermeable top electrode. The gases are formed by electron-induced phase decomposition of P(VDF-TrFE), similar as reported for inorganic ferroelectric materials. When the gas barrier is removed and the waveform is adapted, a fatigue-free ferroelectric capacitor based on P(VDF-TrFE) is realized. The capacitor can be cycled for more than 108 times, approaching the programming cycle endurance of its inorganic ferroelectric counterparts. PMID:24861542

Fatigue-environment interactions in a SiC/Ti-15-3 composite

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Lerch, B. A.

1993-01-01

Load-controlled isothermal and nonisothermal fatigue lives of a (0-deg)s SiC/Ti-15-3 were evaluated at temperatures between 150 and 550 C and a target strain range of about 0.45 percent. In nonisothermal fatigue tests, load was first cycled at minimum temperature and then temperature was cycled at zero load. For fatigue tests with peak temperatures at or above 300 C, fatigue life was dramatically reduced compared to that at 150 C. The shortest life was produced by the nonisothermal test with the greatest temperature range (Delta T = 400 C) and highest peak temperature (T(max) = 550 C). Vacuum testing showed that much of the life reduction under isothermal and nonisothermal conditions was related to environmental effects, although the nature of the fatigue-environment interaction was decidedly different for the isothermal and nonisothermal test cycles which were studied.

Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

NASA Astrophysics Data System (ADS)

Wang, Hong; Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

2014-12-01

Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 108 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines.

Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hong; Lee, Sung Min; Wang, James L.

Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10^8 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and themore » fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications such as piezoelectric fuel injectors in heavy-duty diesel engines.« less

Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

DOE PAGES

Wang, Hong; Lee, Sung Min; Wang, James L.; ...

2014-12-19

Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10^8 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and themore » fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications such as piezoelectric fuel injectors in heavy-duty diesel engines.« less

Fatigue life of fibre reinforced plastics at 295 K after thermal cycling between 295 K and 77 K

NASA Astrophysics Data System (ADS)

Belisario, G.; Caproni, F.; Marchetti, E.

Results of low cycle three-point end fatigue tests at 295 K are reported. These were obtained from fibre reinforced plastics (FRP) flat specimens made of epoxy matrix reinforced with glass rovings only or glass rovings and Kevlar cloth. It is shown that previous thermal cycles between 295 K and 77 K exert an influence on the fatigue life as well on the acoustic emission results.

Climate specific thermomechanical fatigue of flat plate photovoltaic module solder joints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bosco, Nick; Silverman, Timothy J.; Kurtz, Sarah

FEM simulations of PbSn solder fatigue damage are used to evaluate seven cities that represent a variety of climatic zones. It is shown that the rate of solder fatigue damage is not ranked with the cities' climate designations. For an accurate ranking, the mean maximum daily temperature, daily temperature change and a characteristic of clouding events are all required. A physics-based empirical equation is presented that accurately calculates solder fatigue damage according to these three factors. An FEM comparison of solder damage accumulated through service and thermal cycling demonstrates the number of cycles required for an equivalent exposure. For anmore » equivalent 25-year exposure, the number of thermal cycles (-40 degrees C to 85 degrees C) required ranged from roughly 100 to 630 for the cities examined. It is demonstrated that increasing the maximum cycle temperature may significantly reduce the number of thermal cycles required for an equivalent exposure.« less

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

PubMed

Krewerth, D; Weidner, A; Biermann, H

2013-12-01

The present paper illustrates the application of infrared thermal measurements for the investigation of crack initiation point and crack propagation in the high-cycle and the very high-cycle fatigue range of cast AlSi7Mg alloy (A356). The influence of casting defects, their location, size and amount was studied both by fractography and thermography. Besides internal and surface fatigue crack initiation as a further crack initiation type multiple fatigue crack initiation was observed via in situ thermography which can be well correlated with the results from fractography obtained by SEM investigations. In addition, crack propagation was studied by the development of the temperature measured via thermography. Moreover, the frequency influence on high-cycle fatigue behaviour was investigated. The presented results demonstrate well that the combination of fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation in the VHCF regime. Copyright © 2013 Elsevier B.V. All rights reserved.

Experiments of thermomechanical fatigue of SMAs

NASA Astrophysics Data System (ADS)

Lagoudas, Dimitris C.; Miller, David A.

1999-07-01

As SMA wires are gaining in popularity for use as actuators, one constitutive parameter that remain unknown is the thermomechanical fatigue life. Even though the effect of thermal cycles on the transformation characteristics of SMAs has been studied, these teste have not been extended to high number of cycles. In this study, a novel test frame developed to study the thermomechanical fatigue life of SMAs is described. Additionally, a testing protocol is discussed necessary to fully establish the fatigue characteristics of SMAs under various conditions. Initial results of the initial test show a substantial increase in the number of cycles to failure as the applied stress level reduces to approximately 100 MPa.

Effect of autoclave sterilization on the cyclic fatigue resistance of thermally treated Nickel-Titanium instruments.

PubMed

Zhao, D; Shen, Y; Peng, B; Haapasalo, M

2016-10-01

To compare the cyclic fatigue resistance of HyFlex CM, Twisted Files (TF), K3XF, Race, and K3, and evaluate the effect of autoclave sterilization on the cyclic fatigue resistance of these instruments both before and after the files were cycled. Five types of NiTi instruments with similar size 30, .06 taper were selected: HyFlex CM, TF, K3XF, Race and K3. Files were tested in a simulated canal with a curvature of 60° and a radius of 3 mm. The number of cycles to failure of each instrument was determined to evaluate cyclic fatigue resistance. Each type of instruments was randomly divided into four experimental groups: group 1 (n = 20), unsterilized instruments; group 2 (n = 20), pre-sterilized instruments subjected to 10 cycles of autoclave sterilization; group 3 (n = 20), instruments tested were sterilized at 25%, 50% and 75% of the mean cycles to failure as determined in group 1, and then cycled to failure; group 4 (n = 20), instruments cycled in the same manner as group 3 but without sterilization. The fracture surfaces of instruments were examined by scanning electron microscopy (SEM). HyFlex CM, TF and K3XF had significantly higher cyclic fatigue resistance than Race and K3 in the unsterilized group 1 (P < 0.05). Autoclave sterilization significantly increased the MCF of HyFlex CM and K3XF (P < 0.05) both before and after the files were cycled. SEM examination revealed a typical pattern of cyclic fatigue fracture in all instruments. HyFlex CM, TF and K3XF instruments composed of new thermal-treated alloy were more resistant to fatigue failure than Race and K3. Autoclaving extended the cyclic fatigue life of HyFlex CM and K3XF. © 2015 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

NASA Astrophysics Data System (ADS)

Takahashi, Kyouhei; Ogawa, Takeshi

Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

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

NASA Astrophysics Data System (ADS)

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 experimental data for the dual-phase Ti-6Al-4V and were applied to the beta annealed variant in order to estimate stress-life behavior using a small-sample approach. Based on this research, designers should be better able to make reliable estimates of fatigue strength parameters using small-sample testing.

Impact resonance method for damage detection in RC beams strengthened with composites

NASA Astrophysics Data System (ADS)

Gheorghiu, Catalin; Rhazi, Jamal E.; Labossiere, Pierre

2005-05-01

There are numerous successful applications of fibre-reinforced composites for strengthening the civil engineering infrastructure. Most of these repairs are being continuously or intermittently monitored for assessing their effectiveness and safety. The impact resonance method (IRM), a non-destructive technique, utilized in civil engineering exclusively for determining the dynamic concrete properties, could be a valuable and viable damage detection tool for structural elements. The IRM gives useful information about the dynamic characteristics of rectangular and circular concrete members such as beams and columns. In this experimental program, a 1.2-m-long reinforced concrete beam strengthened with a carbon fibre-reinforced polymer (CFRP) plate has been employed. The CFRP-strengthened beam has been loaded in fatigue for two million cycles at 3 Hz. The load amplitude was from 15 to 35% of the anticipated yielding load of the beam. Throughout fatigue testing the cycling was stopped for IRM measurements to be taken. The obtained data provided information about changes in modal properties such as natural frequencies of vibration. These results have shown the successful use of the IRM for detecting fatigue damage in concrete members strengthened with composites.

Influence of dietary nitrate supplementation on physiological and cognitive responses to incremental cycle exercise.

PubMed

Thompson, Kevin G; Turner, Louise; Prichard, Jonathon; Dodd, Fiona; Kennedy, David O; Haskell, Crystal; Blackwell, James R; Jones, Andrew M

2014-03-01

Dietary inorganic nitrate supplementation causes physiological effects which may enhance exercise tolerance. However it is not known whether nitrate might alter cognitive function during exercise. In a double-blind, cross-over study, sixteen subjects ingested either nitrate-rich beetroot juice or a placebo and completed a continuous cycle exercise test involving 20min stages at 50% and 70% V˙O2peak and a final stage at 90% V˙O2peak until volitional exhaustion. Cognitive tasks were completed before, during and after exercise. In the dietary nitrate condition: plasma [nitrite] increased (p<0.01), systolic blood pressure decreased (p<0.05) and there was a trend for a reduced oxygen uptake at 50% V˙O2peak. Tissue oxygenation improved across exercise intensities and exercise tolerance was greater at 90% V˙O2peak (p<0.05). Rating of perceived exertion, energy levels and cognitive performance were similar between conditions with mental fatigue being evident from 70% V˙O2peak onwards (p<0.05). Dietary nitrate supplementation enhanced short-term endurance exercise performance with concomitant mental fatigue but did not improve cognitive performance post-fatigue. Copyright © 2014 Elsevier B.V. All rights reserved.

Assessment of Composite Delamination Self-Healing Under Cyclic Loading

NASA Technical Reports Server (NTRS)

O'Brien, T. Kevin

2009-01-01

Recently, the promise of self-healing materials for enhanced autonomous durability has been introduced using a micro-encapsulation technique where a polymer based healing agent is encapsulated in thin walled spheres and embedded into a base polymer along with a catalyst phase. For this study, composite skin-stiffener flange debonding specimens were manufactured from composite prepreg containing interleaf layers with a polymer based healing agent encapsulated in thin-walled spheres. Constant amplitude fatigue tests in three-point bending showed the effect of self-healing on the fatigue response of the skin-stiffener flange coupons. After the cycling that created debonding, fatigue tests were held at the mean load for 24 hours. For roughly half the specimens tested, when the cyclic loading was resumed a decrease in compliance (increase in stiffness) was observed, indicating that some healing had occurred. However, with continued cycling, the specimen compliance eventually increased to the original level before the hold, indicating that the damage had returned to its original state. As was noted in a prevoius study conducted with specimens tested under monotonically increasing loads to failure, healing achieved via the micro-encapsulation technique may be limited to the volume of healing agent available relative to the crack volume.

Compression fatigue behavior and failure mechanism of porous titanium for biomedical applications.

PubMed

Li, Fuping; Li, Jinshan; Huang, Tingting; Kou, Hongchao; Zhou, Lian

2017-01-01

Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress. The relationship between normalized fatigue strength and fatigue life conforms to a power law. The compression fatigue behavior is characteristic of strain accumulation. Porous titanium experiences uniform deformation throughout the entire sample when fatigue cycle is lower than a critical value (N T ). When fatigue cycles exceed N T , strain accumulates rapidly and a single collapse band forms with a certain angle to the loading direction, leading to the sudden failure of testing sample. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. Porous titanium possesses higher normalized fatigue strength which is in the range of 0.5-0.55 at 10 6 cycles. The reasons for the higher normalized fatigue strength were analyzed based on the microstructure and fatigue failure mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2007-01-01

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

Shot-Peening Sensitivity of Aerospace Materials

DTIC Science & Technology

2007-05-01

19. The beta-STOA titanium , Kt = 1 cyclic fatigue data. 41 Beta-STOA Ti- 6 - 4 Kt = 1.75 - Stress versus Cycles to Failure 80 85 90 95 100 105...The beta-STOA titanium , Kt = 1.75 cyclic fatigue data. Beta-STOA Ti- 6 - 4 Kt = 2.5 - Stress versus Cycles to Failure 60 65 70 75 80 85 90 1.E+03 1... 4 4.2 Phase 2. Fatigue/XRD-RSA/Surface Roughness Assessment ....................................... 6 4.2.1 Fatigue

Accelerated fatigue testing of dentin-composite bond with continuously increasing load.

PubMed

Li, Kai; Guo, Jiawen; Li, Yuping; Heo, Young Cheul; Chen, Jihua; Xin, Haitao; Fok, Alex

2017-06-01

The aim of this study was to evaluate an accelerated fatigue test method that used a continuously increasing load for testing the dentin-composite bond strength. Dentin-composite disks (ϕ5mm×2mm) made from bovine incisor roots were subjected to cyclic diametral compression with a continuously increasingly load amplitude. Two different load profiles, linear and nonlinear with respect to the number of cycles, were considered. The data were then analyzed by using a probabilistic failure model based on the Weakest-Link Theory and the classical stress-life function, before being transformed to simulate clinical data of direct restorations. All the experimental data could be well fitted with a 2-parameter Weibull function. However, a calibration was required for the effective stress amplitude to account for the difference between static and cyclic loading. Good agreement was then obtained between theory and experiments for both load profiles. The in vitro model also successfully simulated the clinical data. The method presented will allow tooth-composite interfacial fatigue parameters to be determined more efficiently. With suitable calibration, the in vitro model can also be used to assess composite systems in a more clinically relevant manner. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1984-01-01

Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

Seasonality of cavitation and frost fatigue in Acer mono Maxim.

PubMed

Zhang, Wen; Feng, Feng; Tyree, Melvin T

2017-12-08

Although cavitation is common in plants, it is unknown whether the cavitation resistance of xylem is seasonally constant or variable. We tested the changes in cavitation resistance of Acer mono before and after a controlled cavitation-refilling and freeze-thaw cycles for a whole year. Cavitation resistance was determined from 'vulnerability curves' showing the percent loss of conductivity versus xylem tension. Cavitation fatigue was defined as a reduction of cavitation resistance following a cavitation-refilling cycle, whereas frost fatigue was caused by a freeze-thaw cycle. A. mono developed seasonal changes in native embolisms; values were relatively high during winter but relatively low and constant throughout the growing season. Cavitation fatigue occurred and changed seasonally during the 12-month cycle; the greatest fatigue response occurred during summer and the weakest during winter, and the transitions occurred during spring and autumn. A. mono was highly resistant to frost damage during the relatively mild winter months; however, a quite different situation occurred during the growing season, as the seasonal trend of frost fatigue was strikingly similar to that of cavitation fatigue. Seasonality changes in cavitation resistance may be caused by seasonal changes in the mechanical properties of the pit membranes. © 2017 John Wiley & Sons Ltd.

EFFECTS OF CYCLIC FLEXURAL FATIGUE ON PORCINE BIOPROSTHETIC HEART VALVE HETEROGRAFT BIOMATERIALS

PubMed Central

Mirnajafi, Ali; Zubiate, Brett; Sacks, Michael S.

2009-01-01

While bioprosthetic heart valves (BHV) remain the primary treatment modality for adult heart valve replacement, continued problems with durability remain. Several studies have implicated flexure as a major damage mode in porcine-derived heterograft biomaterials used in BHV fabrication. While conventional accelerated wear testing can provide valuable insights into BHV damage phenomena, the constituent tissues are subjected to complex, time-varying deformation modes (i.e. tension and flexure), that do not allow for the control of the amount, direction, and location of flexure. Thus, in the present study customized fatigue testing devices were developed to subject circumferentially oriented porcine BHV tissue strips to controlled cyclic flexural loading. By using this approach, we were able to study layer-specific structural damage induced by cyclic flexural tensile and compressive stresses alone. 10×106, 25×106 and 50×106 cycle levels were used, with resulting changes in flexural stiffness and collagen structure assessed. Results indicated that flexural rigidity was markedly reduced after only 10×106 cycles, and progressively decayed at a lower rate with cycle number thereafter. Moreover, the against-curvature fatigue direction induced the most damage, suggesting that the ventricularis and fibrosa layers have low resistance to cyclic flexural compressive and tensile loads, respectively. The histological analyses indicated progressive collagen fiber delamination as early as 10×106 cycles, but otherwise no change in gross collagen orientation. Our results underscore that porcine-derived heterograft biomaterials are very sensitive to flexural fatigue, with delamination of the tissue layers the primary underlying mechanism. This appears to be in contrast to pericardial BHV, wherein high tensile stresses are considered to be the major cause of structural failure. These findings point towards the need for the development of chemical fixation technologies that minimize flexure induced damage to extend porcine heterograft biomaterial durability. PMID:20166221

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, K.L., E-mail: 12klfan@tongji.edu.cn; He, G.Q.; She, M.

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 themore » 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.« less

Nonlinear acoustic measurements ahead of a notch during fatigue

NASA Astrophysics Data System (ADS)

Martin, R. W.; Mooers, R. D.; Hutson, A. L.; Sathish, S.; Blodgett, M. P.

2013-01-01

This paper presents measurements of relative nonlinear acoustic parameter (βrel), ahead of a notch in Al 7075-T651 dog bone samples, subjected to fatigue. It is compared with crack growth measurements on the same samples. Measurements performed on two samples subjected to identical fatigue conditions that failed at vastly different number of fatigue cycles are described. The βrel measurement for both samples as a function of fatigue cycles was fit a Boltzmann curve. The role of changing βrel ahead of a notch is explored as a possible approach for remain life evaluation.

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

NASA Astrophysics Data System (ADS)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

2016-03-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

Low-cycle thermal fatigue

NASA Technical Reports Server (NTRS)

Halford, G. R.

1986-01-01

A state-of-the-art review is presented of the field of thermal fatigue. Following a brief historical review, the concept is developed that thermal fatigue can be viewed as processes of unbalanced deformation and cracking. The unbalances refer to dissimilar mechanisms occurring in opposing halves of thermal fatigue loading and unloading cycles. Extensive data summaries are presented and results are interpreted in terms of the unbalanced processes involved. Both crack initiation and crack propagation results are summarized. Testing techniques are reviewed, and considerable discussion is given to a technique for thermal fatigue simulation, known as the bithermal fatigue test. Attention is given to the use of isothermal life prediction methods for the prediction of thermal fatigue lives. Shortcomings of isothermally-based life prediction methods are pointed out. Several examples of analyses and thermal fatigue life predictions of high technology structural components are presented. Finally, numerous dos and don'ts relative to design against thermal fatigue are presented.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Minutes of the Conference on the International Committee on Aeronautical Fatigue (10th) Held in Melbourne, Australia on May 1967

DTIC Science & Technology

1968-02-01

Effects A room temperature, axial-loading low-cycle fatigue investigation on 2024 -T4 and 7075--T6 aluminum alloys ...Hudson, C. Michael: Investigation of the Effect of Stress Ratio on Fatigue Crack Growth in 7075-T6 Aluminum Alloy . To be presented at Symposium on...Stress Ratio on Fatigue Crack Growth and Mode of Fracture in 2024 -T4 and 7075-T6 Aluminum Alloys in the Low-Cycle Range. Air Force Materials Laboratory

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

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.

2003-01-01

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

Low cycle fatigue behavior of polycrystalline NiAl at 300 and 1000 K

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Noebe, Ronald D.

1993-01-01

The low cycle fatigue behavior of polycrystalline NiAl was determined at 300 and 1000 K - temperatures below and above the brittle- to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on two differently fabricated alloy samples: hot isostatically pressed (HIP'ed) prealloyed powder and hot extruded castings. HIP'ed powder (HP) samples were tested only at 1000 K, whereas the more ductile cast-and-extruded (C+E) NiAl samples were tested at both 1000 and 300 K. Plastic strain ranges of 0.06 to 0.2 percent were used. The C+E NiAl cyclically hardened until fracture, reaching stress levels approximately 60 percent greater than the ultimate tensile strength of the alloy. Compared on a strain basis, NiAl had a much longer fatigue life than other B2 ordered compounds in which fracture initiated at processing-related defects. These defects controlled fatigue life at 300 K, with fracture occurring rapidly once a critical stress level was reached. At 1000 K, above the BDTT, both the C+E and HP samples cyclically softened during most of the fatigue tests in air and were insensitive to processing defects. The processing method did not have a major effect on fatigue life; the lives of the HP samples were about a factor of three shorter than the C+E NiAl, but this was attributed to the lower stress response of the C+E material. The C+E NiAl underwent dynamic grain growth, whereas the HP material maintained a constant grain size during testing. In both materials, fatigue life was controlled by intergranular cavitation and creep processes, which led to fatigue crack growth that was primarily intergranular in nature. Final fracture by overload was transgranular in nature. Also, HP samples tested in vacuum had a life three times longer than their counterparts tested in air and, in contrast to those tested in air, hardened continuously over half of the sample life, thereby indicating an environmentally assisted fatigue damage mechanism. The C+E samples were tested only in air. At 1000 K, NiAl exhibited a superior fatigue life when compared to most superalloys on a plastic strain basis, but was inferior to most superalloys on a stress basis.

Indentation hardness: A simple test that correlates with the dissipated-energy predictor for fatigue-life in bovine pericardium membranes for bioprosthetic heart valves.

PubMed

Tobaruela, Almudena; Rojo, Francisco Javier; García Paez, José María; Bourges, Jean Yves; Herrero, Eduardo Jorge; Millán, Isabel; Alvarez, Lourdes; Cordon, Ángeles; Guinea, Gustavo V

2016-08-01

The aim of this study was to evaluate the variation of hardness with fatigue in calf pericardium, a biomaterial commonly used in bioprosthetic heart valves, and its relationship with the energy dissipated during the first fatigue cycle that has been shown to be a predictor of fatigue-life (García Páez et al., 2006, 2007; Rojo et al., 2010). Fatigue tests were performed in vitro on 24 pericardium specimens cut in a root-to-apex direction. The specimens were subjected to a maximum stress of 1MPa in blocks of 10, 25, 50, 100, 250, 500, 1000 and 1500 cycles. By means of a modified Shore A hardness test procedure, the hardness of the specimen was measured before and after fatigue tests. Results showed a significant correlation of such hardness with fatigue performance and with the energy dissipated in the first cycle of fatigue, a predictor of pericardium durability. The study showed indentation hardness as a simple and reliable indicator of mechanical performance, one which could be easily implemented in improving tissue selection. Copyright © 2016 Elsevier Ltd. All rights reserved.

Experimental Investigation of the Acoustic Nonlinear Behavior in Granular Polymer Bonded Explosives with Progressive Fatigue Damage

PubMed Central

Yang, Zhanfeng; Tian, Yong; Li, Weibin; Zhou, Haiqiang; Zhang, Weibin; Li, Jingming

2017-01-01

The measurement of acoustic nonlinear response is known as a promising technique to characterize material micro-damages. In this paper, nonlinear ultrasonic approach is used to characterize the evolution of fatigue induced micro-cracks in polymer bonded explosives. The variations of acoustic nonlinearity with respect to fatigue cycles in the specimens are obtained in this investigation. The present results show a significant increase of acoustic nonlinearity with respect to fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and fatigue cycles in carbon/epoxy laminates, verifies that an acoustic nonlinear response can be used to evaluate the progressive fatigue damage in the granular polymer bonded explosives. The sensitivity comparison of nonlinear and linear parameters of ultrasonic waves in the specimens shows that nonlinear acoustic parameters are more promising indicators to fatigue induced micro-damage than linear ones. The feasibility study of the micro-damage assessment of polymer bonded explosives by nonlinear ultrasonic technique in this work can be applied to damage identification, material degradation monitoring, and lifetime prediction of the explosive parts. PMID:28773017

Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hong, E-mail: wangh@ornl.gov; Lee, Sung-Min; Wang, James L.

Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10{sup 8} cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatiguemore » index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines.« less

Experimental Investigation of the Acoustic Nonlinear Behavior in Granular Polymer Bonded Explosives with Progressive Fatigue Damage.

PubMed

Yang, Zhanfeng; Tian, Yong; Li, Weibin; Zhou, Haiqiang; Zhang, Weibin; Li, Jingming

2017-06-16

The measurement of acoustic nonlinear response is known as a promising technique to characterize material micro-damages. In this paper, nonlinear ultrasonic approach is used to characterize the evolution of fatigue induced micro-cracks in polymer bonded explosives. The variations of acoustic nonlinearity with respect to fatigue cycles in the specimens are obtained in this investigation. The present results show a significant increase of acoustic nonlinearity with respect to fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and fatigue cycles in carbon/epoxy laminates, verifies that an acoustic nonlinear response can be used to evaluate the progressive fatigue damage in the granular polymer bonded explosives. The sensitivity comparison of nonlinear and linear parameters of ultrasonic waves in the specimens shows that nonlinear acoustic parameters are more promising indicators to fatigue induced micro-damage than linear ones. The feasibility study of the micro-damage assessment of polymer bonded explosives by nonlinear ultrasonic technique in this work can be applied to damage identification, material degradation monitoring, and lifetime prediction of the explosive parts.

A robust signal processing method for quantitative high-cycle fatigue crack monitoring using soft elastomeric capacitor sensors

NASA Astrophysics Data System (ADS)

Kong, Xiangxiong; Li, Jian; Collins, William; Bennett, Caroline; Laflamme, Simon; Jo, Hongki

2017-04-01

A large-area electronics (LAE) strain sensor, termed soft elastomeric capacitor (SEC), has shown great promise in fatigue crack monitoring. The SEC is able to monitor strain changes over a mesoscale structural surface and endure large deformations without being damaged under cracking. Previous tests verified that the SEC is able to detect, localize, and monitor fatigue crack activities under low-cycle fatigue loading. In this paper, to examine the SEC's capability of monitoring high-cycle fatigue cracks, a compact specimen is tested under cyclic tension, designed to ensure realistic crack opening sizes representative of those in real steel bridges. To overcome the difficulty of low signal amplitude and relatively high noise level under high-cycle fatigue loading, a robust signal processing method is proposed to convert the measured capacitance time history from the SEC sensor to power spectral densities (PSD) in the frequency domain, such that signal's peak-to-peak amplitude can be extracted at the dominant loading frequency. A crack damage indicator is proposed as the ratio between the square root of the amplitude of PSD and load range. Results show that the crack damage indicator offers consistent indication of crack growth.

[The influence of autoclave sterilization on surface characteristics and cyclic fatigue resistance of 3 nickel-titanium rotary instruments].

PubMed

Li, Xiang-fen; Zheng, Ping; Xu, Li; Su, Qin

2015-12-01

To investigate the effects of autoclave sterilization on surface characteristics and cyclic fatigue resistance of 3 types of nickel-titanium rotary instruments (K3, Mtwo, ProTaper). Three brands of NiTi rotary endodontic instruments of the same size (tip diameter 0.25 mm and constant 0.06 taper) were selected: K3, Mtwo and Protaper (F2). 24 instruments for each brand were used to evaluate the effects of autoclave sterilization on inner character in the as-received condition and after subjection to 0, 1, 5, and 10 sterilization cycles (6 for each group). Time to fracture (TtF) from the start of the test to the moment of file breakage and the length of the fractured fragment were recorded. Means and standard deviations of TtF and fragment length were calculated. The data was analyzed with SPSS13.0 software package. Another 12 NiTi rotary instruments for each brand were used, 6 subjected to 10 autoclave sterilization cycles and the other as control. Scanning electron microscope was used to observe the changes in surface topography and inner character. For cyclic fatigue resistance, when sterilization was not performed, K3 showed the highest value of TtF means and ProTaper the lowest. The differences between each brand were statistically significant (P<0.05).When disinfection was performed, K3 brand showed greater fatigue resistance in comparison with the control when autoclave sterilization cycled 5 times and 10 times. The difference between 10 cycles of sterilization and the control was statistically significant (P<0.05); ProTaper brand showed significantly greater fatigue resistance in all the disinfected groups compared with the control (P<0.05) and 5 cycles of sterilization led to the greatest increment; The fatigue resistance of Mtwo brands increased with sterilization cycles and the difference between 5/10 cycles and the control were statistically significant (P<0.05). For surface characteristics, under scanning electron microscope, surface and inner imperfections in all instruments were intensified greatly after 10 cycles of sterilization. Cycle fatigue resistance is different among instruments of different brands. Autoclave sterilization may increase fatigue resistance of the 3 brands. Autoclave sterilization may increase the surface roughness and inner defects in cross section.

The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study.

PubMed

Daratsianos, Nikolaos; Musabegovic, Ena; Reimann, Susanne; Grüner, Manfred; Jäger, Andreas; Bourauel, Christoph

2013-05-01

To describe the effect of fatigue on the strength of the bracket-adhesive-enamel complex and characterize the fatigue behavior of the materials tested. Upper central incisor brackets (Discovery(®), Dentaurum) were bonded with a light-curing (Transbond XT™, 3M Unitek) and a chemically-curing adhesive (Concise™, 3M Unitek) on bovine teeth embedded in cylindrical resign bases and stored in water at 37(±2)°C for 24 (±2)h. The first 15 specimens were tested with a universal testing machine ZMART.PRO(®) (Zwick GmbH & Co. KG, Ulm, Germany) for ultimate shear bond strength according to the DIN-13990-2-standard. The remaining three groups of 20 specimens underwent fatigue staircase testing of 100, 1000 and 3000 cycles at 1Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing. The fatigued specimens showed decreased shear strength with both adhesives at all cycle levels. The shear strength after fatigue for 100, 1000 and 3000 cycles was in the Concise™-groups 34.8%, 59.0%, 47.3% and in the Transbond™ XT-groups 33.6%, 23.1%, 27.3% relative to the ultimate shear strength. The fatigue life of the Concise™-groups decreased with increasing stress and Transbond™ XT showed lower fatigue ratio with no obvious trend. The specimens bonded with Transbond™ XT showed typically favorable fracture modes in contrary to Concise™. Fatigue of the bracket-adhesive-enamel complex decreased its shear strength. The staircase method can provide a standardized experimental protocol for fatigue studies, however testing at various cycle numbers is recommended. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Strain-cycling fatigue behavior of ten structural metals tested in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K)

NASA Technical Reports Server (NTRS)

Nachtigall, A. J.

1974-01-01

Strain-cycling fatigue behavior of 10 different structural alloys and metals was investigated in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K). At high cyclic lives, fatigue resistance increased with decreasing temperature for all the materials investigated. At low cyclic lives, fatigue resistance generally decreased with decreasing temperature for the materials investigated. Only for Inconel 718 did fatigue resistance increase with decreasing temperature over the entire life range investigated. Comparison of the experimental fatigue behavior with that predicted by the Manson method of universal slopes showed that the fatigue behavior of these materials can be predicted for cryogenic temperatures by using material tensile properties obtained at those same temperatures.

Uniaxial low cycle fatigue behavior for pre-corroded 16MND5 bainitic steel in simulated pressurized water reactor environment

NASA Astrophysics Data System (ADS)

Chen, Xu; Ren, Bin; Yu, Dunji; Xu, Bin; Zhang, Zhe; Chen, Gang

2018-06-01

The effects of uniaxial tension properties and low cycle fatigue behavior of 16MND5 bainitic steel cylinder pre-corroded in simulated pressurized water reactor (PWR) were investigated by fatigue at room temperature in air and immersion test system, scanning electron microscopy (SEM), energy disperse spectroscopy (EDS). The experimental results indicated that the corrosion fatigue lives of 16MND5 specimen were significantly affected by the strain amplitude and simulated PWR environments. The compositions of corrosion products were complexly formed in simulated PWR environments. The porous corrosion surface of pre-corroded materials tended to generate pits as a result of promoting contact area to the fresh metal, which promoted crack initiation. For original materials, the fatigue cracks initiated at inclusions imbedded in the micro-cracks. Moreover, the simulated PWR environments degraded the mechanical properties and low cycle fatigue behavior of 16MND5 specimens remarkably. Pre-corrosion of 16MND5 specimen mainly affected the plastic term of the Coffin-Manson equation.

The Effect of Fatigue-Induced Changes in Eggbeater-Kick Kinematics on Performance and Risk of Injury.

PubMed

Oliveira, Nuno; Saunders, David H; Sanders, Ross H

2016-01-01

To investigate the effects of fatigue on the vertical force and kinematics of the lower limbs during maximal water polo eggbeater kicking. Twelve male water polo players maintained as high a position as possible while performing the eggbeater kick with the upper limbs raised out of the water until they were unable to keep the top of the sternum (manubrium) above water. Data comprising 27 complete eggbeater-kick cycles were extracted corresponding to 9 cycles of the initial nonfatigued (0%), 50% time point (50%), and final fatigued (100%) periods of the trial. Vertical force, foot speed, and hip-, knee-, and ankle-joint angles were calculated. Mean vertical force (0%, 212.2 N; 50%, 184.5 N; 100%, 164.3 N) progressively decreased with time. Speed of the feet (0.4 m/s), hip abduction (2.9°), and flexion (3.6°) decreased with fatigue, while hip internal rotation (3.6°) and ankle inversion (4°) increased with fatigue. Average angular velocity decreased for all joint motions. Eggbeater-kick performance decreases with fatigue. Inability to maintain foot speeds and hip and ankle actions with progressing fatigue diminishes the ability of the player to produce vertical force during the cycle. Increased internal rotation of the hip when fatigued and the large eversion/abduction of the ankle during the cycle may be predisposing factors for the prevalence of patellofemoral pain syndrome observed among eggbeater-kick performers. Appropriate training interventions that can limit the effects of fatigue on performance and injury risk should be considered.

Damage Evolution and Life Prediction of Cross-Ply C/SiC Ceramic-Matrix Composite under Cyclic Fatigue Loading at Room Temperature and 800 °C in Air

PubMed Central

Li, Longbiao

2015-01-01

The damage evolution and life prediction of cross-ply C/SiC ceramic-matrix composite (CMC) under cyclic-fatigue loading at room temperature and 800 °C in air have been investigated using damage parameters derived from fatigue hysteresis loops, i.e., fatigue hysteresis modulus and fatigue hysteresis loss energy. The experimental fatigue hysteresis modulus and fatigue hysteresis loss energy degrade with increasing applied cycles attributed to transverse cracks in the 90° plies, matrix cracks and fiber/matrix interface debonding in the 0° plies, interface wear at room temperature, and interface and carbon fibers oxidation at 800 °C in air. The relationships between fatigue hysteresis loops, fatigue hysteresis modulus and fatigue hysteresis loss energy have been established. Comparing experimental fatigue hysteresis loss energy with theoretical computational values, the fiber/matrix interface shear stress corresponding to different cycle numbers has been estimated. It was found that the degradation rate at 800 °C in air is much faster than that at room temperature due to serious oxidation in the pyrolytic carbon (PyC) interphase and carbon fibers. Combining the fiber fracture model with the interface shear stress degradation model and the fibers strength degradation model, the fraction of broken fibers versus the cycle number can be determined for different fatigue peak stresses. The fatigue life S-N curves of cross-ply C/SiC composite at room temperature and 800 °C in air have been predicted. PMID:28793728

Damage Evolution and Life Prediction of Cross-Ply C/SiC Ceramic-Matrix Composite under Cyclic Fatigue Loading at Room Temperature and 800 °C in Air.

PubMed

Li, Longbiao

2015-12-09

The damage evolution and life prediction of cross-ply C/SiC ceramic-matrix composite (CMC) under cyclic-fatigue loading at room temperature and 800 °C in air have been investigated using damage parameters derived from fatigue hysteresis loops, i.e. , fatigue hysteresis modulus and fatigue hysteresis loss energy. The experimental fatigue hysteresis modulus and fatigue hysteresis loss energy degrade with increasing applied cycles attributed to transverse cracks in the 90° plies, matrix cracks and fiber/matrix interface debonding in the 0° plies, interface wear at room temperature, and interface and carbon fibers oxidation at 800 °C in air. The relationships between fatigue hysteresis loops, fatigue hysteresis modulus and fatigue hysteresis loss energy have been established. Comparing experimental fatigue hysteresis loss energy with theoretical computational values, the fiber/matrix interface shear stress corresponding to different cycle numbers has been estimated. It was found that the degradation rate at 800 °C in air is much faster than that at room temperature due to serious oxidation in the pyrolytic carbon (PyC) interphase and carbon fibers. Combining the fiber fracture model with the interface shear stress degradation model and the fibers strength degradation model, the fraction of broken fibers versus the cycle number can be determined for different fatigue peak stresses. The fatigue life S-N curves of cross-ply C/SiC composite at room temperature and 800 °C in air have been predicted.

Grainex Mar-M 247 Turbine Disk Life Study for NASA's High Temperature High Speed Turbine Seal Test Facility

NASA Technical Reports Server (NTRS)

Delgado, Irebert R.

2015-01-01

An experimental and analytical fatigue life study was performed on the Grainex Mar-M 247 disk used in NASA s Turbine Seal Test Facility. To preclude fatigue cracks from growing to critical size in the NASA disk bolt holes due to cyclic loading at severe test conditions, a retirement-for-cause methodology was adopted to detect and monitor cracks within the bolt holes using eddy-current inspection. For the NASA disk material that was tested, the fatigue strain-life to crack initiation at a total strain of 0.5 percent, a minimum to maximum strain ratio of 0, and a bolt hole temperature of 649 C was calculated to be 665 cycles using -99.95 percent prediction intervals. The fatigue crack propagation life was calculated to be 367 cycles after implementing a safety factor of 2 on life. Thus, the NASA disk bolt hole total life or retirement life was determined to be 1032 cycles at a crack depth of 0.501 mm. An initial NASA disk bolt hole inspection at 665 cycles is suggested with 50 cycle inspection intervals thereafter to monitor fatigue crack growth.

A Predictive Framework for Thermomechanical Fatigue Life of High Silicon Molybdenum Ductile Cast Iron Based on Considerations of Strain Energy Dissipation

NASA Astrophysics Data System (ADS)

Avery, Katherine R.

Isothermal low cycle fatigue (LCF) and anisothermal thermomechanical fatigue (TMF) tests were conducted on a high silicon molybdenum (HiSiMo) cast iron for temperatures up to 1073K. LCF and out-of-phase (OP) TMF lives were significantly reduced when the temperature was near 673K due to an embrittlement phenomenon which decreases the ductility of HiSiMo at this temperature. In this case, intergranular fracture was predominant, and magnesium was observed at the fracture surface. When the thermal cycle did not include 673K, the failure mode was predominantly transgranular, and magnesium was not present on the fracture surface. The in-phase (IP) TMF lives were unaffected when the thermal cycle included 673K, and the predominant failure mode was found to be transgranular fracture, regardless of the temperature. No magnesium was present on the IP TMF fracture surfaces. Thus, the embrittlement phenomenon was found to contribute to fatigue damage only when the temperature was near 673K and a tensile stress was present. To account for the temperature- and stress-dependence of the embrittlement phenomenon on the TMF life of HiSiMo cast iron, an original model based on the cyclic inelastic energy dissipation is proposed which accounts for temperature-dependent differences in the rate of fatigue damage accumulation in tension and compression. The proposed model has few empirical parameters. Despite the simplicity of the model, the predicted fatigue life shows good agreement with more than 130 uniaxial low cycle and thermomechanical fatigue tests, cyclic creep tests, and tests conducted at slow strain rates and with hold times. The proposed model was implemented in a multiaxial formulation and applied to the fatigue life prediction of an exhaust manifold subjected to severe thermal cycles. The simulation results show good agreement with the failure locations and number of cycles to failure observed in a component-level experiment.

The effect of cyclic loading on the irradiation hardening of type 316L stainless steel

NASA Astrophysics Data System (ADS)

Scholz, R.

1997-01-01

Strain controlled fatigue tests have been performed in torsion on annealed type 316L stainless steel irradiated with 19 MeV deuterons at 400°C for shear strain ranges between 0.95% and 1.4%. The irradiation hardening of the material was suppressed to a great extent for continuous cycling conditions in comparison to hold time tests.

Mechanisms of Recovering Low Cycle Fatigue Damage in Incoloy 901.

DTIC Science & Technology

1979-01-01

crack growth rate, da/dN, of 0.27 vim/cycle or 1.07 x 10- 4 in./cycle. Macha has determined crack growth rates as a function of AK at 400°F and 6000F...Cleveland, Ohio (1963). 61. T. J. Dolan, "Designing Structures to Resist Low-Cycle Fatigue," Metals Eng. Qtrly 10, 18-25 (November 1970). 62. D. Macha

Ultrasonic Corrosion Fatigue Behavior of High Strength Austenitic Stainless Steels

NASA Astrophysics Data System (ADS)

Ebara, R.; Yamaguchi, Y.; Kanei, D.; Yamamoto, Y.

Ultrasonic corrosion fatigue tests were conducted for high strength austenitic stainless steels such as YUS270 and SUS304N2 in 3%NaCl aqueous solution. The reduction of giga-cycle corrosion fatigue strength of YUS270 and SUS304N2 was not observed at all, while the reduction of corrosion fatigue life was observed at higher stress amplitude. Corrosion pit was observed on corrosion fatigue crack initiation area. Striation was predominantly observed on crack propagation area in air and in 3% NaCl aqueous solution. The reduction of corrosion fatigue strength of high strength austenitic stainless steels such as YUS270 and SUS304N2 is due to the corrosion pit formation at corrosion fatigue crack initiation area. It can be concluded that the higher the ultimate tensile strength of austenitic stainless steels the higher the giga-cycle corrosion fatigue strength in 3%NaCl aqueous solution is.

Characterization of fatigue behavior of 2-D woven fabric reinforced ceramic matrix composite at elevated temperature. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Groner, D.J.

This study investigated the fatigue behavior and associated damage mechanisms in notched and unnotched enhanced SiC/SiC ceramic matrix composite specimens at 1100 deg C. Stiffness degradation, strain variation, and hysteresis were evaluated to characterize material behavior. Microscopic examination was performed to characterize damage mechanisms. During high cycle/low stress fatigue tests, far less fiber/matrix interface debond was evident than in low cycle/high stress fatigue tests. Notched specimens exhibited minimal stress concentration during monotonic tensile testing and minimal notch sensitivity during fatigue testing. Damage mechanisms were also similar to unnotched.

A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

NASA Astrophysics Data System (ADS)

Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

2011-06-01

Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

The effect of advanced ultrasonic forging on fatigue fracture mechanisms of welded Ti-6A1-4V alloy

NASA Astrophysics Data System (ADS)

Smirnova, A.; Pochivalov, Yu.; Panin, V.; Panin, S.; Eremin, A.; Gorbunov, A.

2017-12-01

The current study is devoted to application of advanced postwelding ultrasonic forging to joints formed by laser welding of Ti-6A1-4V alloy in order to enhance their mechanical properties and fatigue durability. Low cycle fatigue tests were performed via digital image correlation technique used to obtain strain fields and in situ characterization of deformation, crack growth and fracture. Fracture surfaces were studied by SEM analysis accompanied with calculation of fracture patterns percentage. The fatigue tests demonstrate the high increase in the number of cycles until fracture (from 17 000 to 32 000 cycles) which could be explained by high ductility of welded material after treatment. This leads to lower fatigue crack growth rate due to higher energy dissipation. The obtained effect is attributable only for small cracks on micro-/mesoscales and fails to play a significant role for macro cracks.

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

NASA Astrophysics Data System (ADS)

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

2015-07-01

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

Failure probability of three designs of zirconia crowns

PubMed Central

Ramos, G. Freitas; Monteiro, E. Barbosa Carmona; Bottino, M.A.; Zhang, Y.; de Melo, R. Marques

2015-01-01

Objectives This study utilized a 2-parameter Weibull analysis for evaluation of lifetime of fully or partially porcelain-/glaze-veneered zirconia crowns after fatigue test. Methods Sixty first molars were selected and prepared for full-coverage crowns with three different designs(n = 20): Traditional –crowns with zirconia framework covered with feldspathic porcelain; Modified– crowns partially covered with veneering porcelain; and Monolithic–full-contour zirconia crowns. All specimens were treated with a glaze layer. Specimens were subjected to mechanical cycling (100N, 3Hz) with a piston with hemispherical tip (Ø=6 mm) until the specimens failed or up to 2×106 cycles. Every 500,000 cycles intervals, the fatigue tests were interrupted, and stereomicroscopy (10 X) was used to inspect the specimens for damage. We performed Weibull analysis of interval data to calculate the number of failures in each interval. Results The types and number of failures according to the groups were: cracking (Traditional-13, Modified-6) and chipping (Traditional-4) of the feldspathic porcelain, followed by delamination (Traditional-1) at the veneer/core interface and debonding (Monollithic-2) at the cementation interface. Weibull parameters (beta, scale; and eta, shape), with a two-sided confidence interval of 95%, were: Traditional – 1.25 and 0.9 × 106cycles; Modified– 0.58 and 11.7 × 106 cycles; and Monolithic – 1.05 and 16.5 × 106 cycles. Traditional crowns showed greater susceptibility to fatigue, the Modified group presented higher propensity to early failures, and the Monolithic group showed no susceptibility to fatigue. The Modified and Monolithic groups presented the highest number of crowns with no failures after the fatigue test. Conclusions The three crown designs presented significantly different behaviors under fatigue. The Modified and the Monolithic groups presented less probability to failure after 2×106cycles. PMID:26509988

Influence of the height of the external hexagon and surface treatment on fatigue life of commercially pure titanium dental implants.

PubMed

Gil, Francisco Javier; Aparicio, Conrado; Manero, Jose M; Padros, Alejandro

2009-01-01

This study evaluated the effect of external hexagon height and commonly applied surface treatments on the fatigue life of titanium dental implants. Electropolished commercially pure titanium dental implants (seven implants per group) with three different external hexagon heights (0.6, 1.2, and 1.8 mm) and implants with the highest external hexagon height (1.8 mm) and different surface treatments (electropolishing, grit blasting with aluminium oxide, and acid etching with sulfuric acid) were tested to evaluate their mechanical fatigue life. To do so, 10-Hz triangular flexural load cycles were applied at 37 degrees C in artificial saliva, and the number of load cycles until implant fracture was determined. Tolerances of the hexagon/abutment fit and implant surface roughness were analyzed by scanning electron microscopy and light interferometry. Transmission electron microscopy and electron diffraction analyses of titanium hydrides were performed. First, the fatigue life of implants with the highest hexagon (8,683 +/- 978 load cycles) was more than double that of the implants with the shortest hexagons (3,654 +/- 789 load cycles) (P < .02). Second, the grit-blasted implants had the longest fatigue life of the tested materials (21,393 +/- 2,356 load cycles), which was significantly greater than that of the other surfaces (P < .001). The compressive surface residual stresses induced when blasting titanium are responsible for this superior mechanical response. Third, precipitation of titanium hydrides in grain boundaries of titanium caused by hydrogen adsorption from the acid solution deteriorates the fatigue life of acid-etched titanium dental implants. These implants had the shortest fatigue life (P < .05). The fatigue life of threaded root-form dental implants varies with the height of the external hexagon and/or the surface treatment of the implant. An external hexagon height of 1.8 mm and/or a blasting treatment appear to significantly increase fatigue life of dental implants.

Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

NASA Technical Reports Server (NTRS)

Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

1976-01-01

During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The zirconium in this alloy was not evenly distributed in the chamber materials. The life that was achieved was nominally the same as would have been predicted from OFHC copper isothermal test data.

The ultimate state of polymeric materials and laminated and fibrous composites under asymmetric high-cycle loading

NASA Astrophysics Data System (ADS)

Golub, V. P.; Pogrebniak, A. D.; Kochetkova, E. S.

2008-01-01

The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered. The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally.

Constant and variable amplitude ultrasonic fatigue of 2024-T351 aluminium alloy at different load ratios.

PubMed

Mayer, H; Fitzka, M; Schuller, R

2013-12-01

Ultrasonic fatigue testing equipment is presented that is capable of performing constant amplitude (CA) and variable amplitude (VA) experiments at different constant load ratios. This equipment is used to study cyclic properties of aluminium alloy 2024-T351 in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime at load ratios R=-1 and R=0.5. CA loading does not reveal a fatigue limit below 10¹⁰ cycles. Cracks leading to VHCF failure start at broken constituent particles. Specimens that survived more than 10¹⁰ cycles at R=-1 contain non-propagating cracks of lengths below grain size. Resonance frequency and nonlinearity parameter β(rel) show changes of vibration properties of specimens at low fractions of their VHCF lifetime. VA lifetimes are measured in the HCF and VHCF regime and compared with Miner calculations. Damage sums decrease with decreasing load (and increasing mean lifetimes) and are lower for R=0.5 than R=-1. Copyright © 2013 Elsevier B.V. All rights reserved.

Preliminary study of thermomechanical fatigue of polycrystalline MAR-M 200

NASA Technical Reports Server (NTRS)

Bill, R. C.; Verrilli, M. J.; Mcgaw, M. A.; Halford, G. R.

1984-01-01

Thermomechanical fatigue (TMF) experiments were conducted on polycrystalline MAR-M 200 over a cyclic temperature range of 500 to 1000 C. Inelastic strain ranges of 0.03 to 0.2 percent were imposed on the specimens. The TMF lives were found to be significantly shorter than isothermal low-cycle-fatigue (LCF) life at the maximum cycle temperature, and in-phase cycling was more damaging than out-of-phase cycling. Extensive crack tip oxidation appeared to play a role in promoting the severity of in-phase cycling. Carbide particle - matrix interface cracking was also observed after in-phase TMF cycling. The applicability of various life prediction models to the TMF results obtained was assessed. It was concluded that current life prediction models based on isothermal data as input must be modified to be applicable to the TMF results.

Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends

NASA Astrophysics Data System (ADS)

Coyle, Richard J.; Sweatman, Keith; Arfaei, Babak

2015-09-01

Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. The electronic packaging industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu alloys first established as replacements for eutectic SnPb. This paper discusses the results from Pb-free solder joint reliability programs sponsored by two industry consortia. The characteristic life in accelerated thermal cycling is reported for 12 different Pb-free solder alloys and a SnPb control in 9 different accelerated thermal cycling test profiles in terms of the effects of component type, accelerated thermal cycling profile and dwell time. Microstructural analysis on assembled and failed samples was performed to investigate the effect of initial microstructure and its evolution during accelerated thermal cycling test. A significant finding from the study is that the beneficial effect of Ag on accelerated thermal cycling reliability (measured by characteristic lifetime) diminishes as the severity of the accelerated thermal cycling, defined by greater ΔT, higher peak temperature, and longer dwell time increases. The results also indicate that all the Pb-free solders are more reliable in accelerated thermal cycling than the SnPb alloy they have replaced. Suggestions are made for future work, particularly with respect to the continued evolution of alloy development for emerging application requirements and the value of using advanced analytical methods to provide a better understanding of the effect of microstructure and its evolution on accelerated thermal cycling performance.

Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components

NASA Technical Reports Server (NTRS)

Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.

1989-01-01

Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.

Effect of load ratio on fatigue crack propagation behavior of solid-solution-strengthened Ni-based superalloys at elevated temperature

NASA Astrophysics Data System (ADS)

Ma, Longzhou; Roy, Shawoon K.

2013-04-01

The fatigue crack propagation (FCP) behavior of two solid-solution-strengthened Ni-based superalloys, INCONEL 617 and HAYNES 230, were studied simultaneously in laboratory air using a constant stress intensity factor (K)-controlled mode with different load ratios (R-ratio) at 700 °C. The FCP tests were performed in both cycle and time-dependent FCP domains to examine the effect of R-ratio on the FCP rate, da/dn. For cycle-dependent FCP test, a 1-s sinusoidal fatigue was applied for a compact tension (CT) specimen of INCONEL 617 and HAYNES 230 to measure their FCP rates. For time-dependent FCP test, a 3-s sinusoidal fatigue with a hold time of 300 s at maximum load was applied. Both cycle/time-dependent FCP behaviors were characterized and analyzed. The results showed that increasing R-ratio would introduce the fatigue incubation and decrease the FCP rates at cycle-dependent FCP tests. On the contrary, fatigue incubation was not observed at time-dependent FCP tests for both INCONEL 617 and HAYNES 230 at each tested R-ratio, suggesting that association of maximum load (Kmax) with crack tip open displacement (CTOD) and environmental factor governed the FCP process. Also, for time-dependent FCP, HAYNES 230 showed lower FCP rates than INCONEL 617 regardless of R-ratio. However, for cycle-dependent FCP, HAYNES 230 showed the lower FCP rates only at high R-ratios. Fracture surface of specimens were examined using SEM to investigate the cracking mechanism under cycle/time-dependent FCP condition with various R-ratios.

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

NASA Astrophysics Data System (ADS)

Fukuoka, C.; Nakagawa, Y. G.; Lance, J. J.; Pangborn, R. N.

1996-12-01

The objective of this work is to evaluate the damage induced below and above the fatigue limit (Δ σ t =360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue test bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.

Acute recovery from exercise in people with multiple sclerosis: an exploratory study on the effect of exercise intensities.

PubMed

Collett, Johnny; Meaney, Andy; Howells, Ken; Dawes, Helen

2017-03-01

Purpose A better understanding of how people with multiple sclerosis (pwMS) recover from exercise may help inform interventions. Methods We explored physiological and perceptual responses following exercise of different intensities, using a crossover exposure-response design, in 14 adults with multiple sclerosis (MS) and 9 controls. A cycling exercise test determined maximum capacity (Wpeak). Participants then performed 20-min exercise sessions relative to Wpeak (random order separated by 7 days): (1) 45% and (2) 60% continuous cycling and (3) 90% intermittent cycling (30 s cycling, 30 s rest). During a 45-min recovery period, tympanic temperature (Temp°C), exertion in breathing (RPEbr) and legs (RPEleg), and cortical excitability (MEParea) were measured. Results Eleven pwMS and eight controls completed the study. Controls performed better on the exercise test (p < 0.05), thus more absolute work during subsequent sessions. PwMS took longer to recover RPEleg with recovery time increasing with intensity (45%-6 min; 60%-15 min; 90%-35 min) and correlating with Temp°C. MEParea was significantly depressed in both groups at 45% and 60% (p < 0.001), in the MS group this also correlated with RPEleg. Conclusions Feelings of leg exertion may persist after exercise in some pwMS, especially at high intensities. This may relate to body temperature and, after continuous exercise, cortical excitability. These results support considering the recovery period post exercise and provide an insight into potential correlates of post-exercise fatigue. Implications for Rehabilitation A better understanding of how pwMS recover following exercise may help inform exercise prescription a long side fatigue management. This study showed that, in pwMS, the time taken to recover from feelings of leg fatigue increased with the intensity of the exercise session rather that total work performed and was related to increase in body temperature. The results of this relatively small study support the need to consider a recovery period after exercise and provide an insight into potential physiological correlates.

Fatigue Analysis of Notched Laminates: A Time-Efficient Macro-Mechanical Approach

NASA Technical Reports Server (NTRS)

Naghipour, P.; Pineda, E. J.; Bednarcyk, B. A.; Arnold, S. M.; Waas, A. M.

2016-01-01

A coupled transversely isotropic deformation and damage fatigue model is implemented within the finite element method and was utilized along with a static progressive damage model to predict the fatigue life, stiffness degradation as a function of number of cycles, and post-fatigue tension and compression response of notched, multidirectional laminates. Initially, the material parameters for the fatigue model were obtained utilizing micromechanics simulations and the provided [0], [90] and [plus or minus 45] experimental composite laminate S-N (stress-cycle) data. Within the fatigue damage model, the transverse and shear properties of the plies were degraded with an isotropic scalar damage variable. The damage in the longitudinal (fiber) ply direction was suppressed, and only the strength of the fiber was degraded as a function of fatigue cycles. A maximum strain criterion was used to capture the failure in each element, and once this criterion was satisfied, the longitudinal stiffness of the element was decreased by a factor of 10 (sup 4). The resulting, degraded properties were then used to calculate the new stress state. This procedure was repeated until final failure of the composite laminate was achieved or a specified number of cycles reached. For post-fatigue tension and compression behavior, four internal state variables were used to control the damage and failure. The predictive capability of the above-mentioned approach was assessed by performing blind predictions of the notched multidirectional IM7/977-3 composite laminates response under fatigue and post-fatigue tensile and compressive loading, followed by a recalibration phase. Although three different multidirectional laminates were analyzed in the course of this study, only detailed results (i.e., stiffness degradation and post-fatigue stress-train curves as well as damage evolution states for a single laminate ([30/60/90/minus 30/minus 60] (sub 2s)) are discussed in detail here.

Combined high vacuum/high frequency fatigue tester

NASA Technical Reports Server (NTRS)

Honeycutt, C. R.; Martin, T. F.

1971-01-01

Apparatus permits application of significantly greater number of cycles or equivalent number of cycles in shorter time than conventional fatigue test machines. Environment eliminates problems associated with high temperature oxidation and with sensitivity of refractory alloy behavior to atmospheric contamination.

Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castelluccio, Gustavo M.; Musinski, William D.; McDowell, David L.

Advances in higher resolution experimental techniques have shown that metallic materials can develop fatigue cracks under cyclic loading levels significantly below the yield stress. Indeed, the traditional notion of a fatigue limit can be recast in terms of limits associated with nucleation and arrest of fatigue cracks at the microstructural scale. Though fatigue damage characteristically emerges from irreversible dislocation processes at sub-grain scales, the specific microstructure attributes, environment, and loading conditions can strongly affect the apparent failure mode and surface to subsurface transitions. This paper discusses multiple mechanisms that occur during fatigue loading in the high cycle fatigue (HCF) tomore » very high cycle fatigue (VHCF) regimes. We compare these regimes, focusing on strategies to bridge experimental and modeling approaches exercised at multiple length scales and discussing particular challenges to modeling and simulation regarding microstructure-sensitive fatigue driving forces and thresholds. Finally, we discuss some of the challenges in predicting the transition of failure mechanisms at different stress and strain amplitudes.« less

Fatigue Behavior of Inconel 718 TIG Welds

NASA Astrophysics Data System (ADS)

Alexopoulos, Nikolaos D.; Argyriou, Nikolaos; Stergiou, Vasillis; Kourkoulis, Stavros K.

2014-08-01

Mechanical behavior of reference and TIG-welded Inconel 718 specimens was examined in the present work. Tensile, constant amplitude fatigue, and fracture toughness tests were performed in ambient temperature for both, reference and welded specimens. Microstructure revealed the presence of coarse and fine-grained heat-affected zones. It has been shown that without any post-weld heat treatment, welded specimens maintained their tensile strength properties while their ductility decreased by more than 40%. It was found that the welded specimens had lower fatigue life and this decrease was a function of the applied fatigue maximum stress. A 30% fatigue life decrease was noticed in the high cycle fatigue regime for the welded specimens while this decrease exceeded 50% in the low cycle fatigue regime. Cyclic stress-strain curves showed that Inconel 718 experiences a short period of hardening followed by softening for all fatigue lives. Cyclic fatigue response of welded specimens' exhibited cyclically stable behavior. Finally, a marginal decrease was noticed in the Mode I fracture toughness of the welded specimens.

Computational micromechanics of fatigue of microstructures in the HCF–VHCF regimes

DOE PAGES

Castelluccio, Gustavo M.; Musinski, William D.; McDowell, David L.

2016-05-19

Advances in higher resolution experimental techniques have shown that metallic materials can develop fatigue cracks under cyclic loading levels significantly below the yield stress. Indeed, the traditional notion of a fatigue limit can be recast in terms of limits associated with nucleation and arrest of fatigue cracks at the microstructural scale. Though fatigue damage characteristically emerges from irreversible dislocation processes at sub-grain scales, the specific microstructure attributes, environment, and loading conditions can strongly affect the apparent failure mode and surface to subsurface transitions. This paper discusses multiple mechanisms that occur during fatigue loading in the high cycle fatigue (HCF) tomore » very high cycle fatigue (VHCF) regimes. We compare these regimes, focusing on strategies to bridge experimental and modeling approaches exercised at multiple length scales and discussing particular challenges to modeling and simulation regarding microstructure-sensitive fatigue driving forces and thresholds. Finally, we discuss some of the challenges in predicting the transition of failure mechanisms at different stress and strain amplitudes.« less

Runners maintain locomotor-respiratory coupling following isocapnic voluntary hyperpnea to task failure.

PubMed

Stickford, Abigail S L; Stickford, Jonathon L; Tanner, David A; Stager, Joel M; Chapman, Robert F

2015-11-01

Evidence has long suggested that mammalian ventilatory and locomotor rhythms are linked, yet determinants and implications of locomotor-respiratory coupling (LRC) continue to be investigated. Anecdotally, respiratory muscle fatigue seen at the end of heavy exercise may result in an uncoupling of movement-ventilation rhythms; however, there is no scientific evidence to substantiate this claim. We sought to determine whether or not fatigue of the respiratory muscles alters locomotor-respiratory coupling patterns typically observed in highly trained individuals while running. A related query was to examine the relationship between the potential changes in LRC and measures of running economy. Twelve male distance runners ran at four submaximal workloads (68-89 % VO2peak) on two separate days while LRC was quantified. One LRC trial served as a control (CON), while the other was performed following an isocapnic voluntary hyperpnea to task failure to induce respiratory muscle fatigue (FT+). LRC was assessed as stride-to-breathing frequency ratios (SF/fB) and degree of LRC (percentage of breaths occurring during the same decile of the step cycle). Hyperpnea resulted in significant declines in maximal voluntary inspiratory (MIP) and expiratory (MEP) mouth pressures (ΔMIP = -10 ± 12 cm H2O; ΔMEP = -6 ± 9 cm H2O). There were no differences in minute ventilation between CON and FT+ (CON, all speeds pooled = 104 ± 25 L min(-1); FT+ pooled = 106 ± 23 L min(-1)). Stride frequency was not different between trials; however, breathing frequency was significantly greater during FT+ compared to CON at all speeds (CON pooled = 47 ± 10 br min(-1); FT+ pooled = 52 ± 9 br min(-1)), resulting in smaller corresponding SF/fB. Yet, the degree of LRC was the same during CON and FT+ (CON pooled = 63 ± 15 %; FT+ pooled = 64 ± 18 %). The results indicate that trained runners are able to continue entraining breath and step cycles, despite marked changes in exercise breathing frequency, after a fatiguing hyperpnea challenge.

Investigation of the effects of manufacturing variations and materials on fatigue crack detection methods in gear teeth

NASA Technical Reports Server (NTRS)

Wheitner, Jeffrey A.; Houser, Donald R.

1994-01-01

The fatigue life of a gear tooth can be thought of as the sum of the number of cycles required to initiate a crack, N(sub i), plus the number of cycles required to propagate the crack to such a length that fracture occurs, N(sub p). The factors that govern crack initiation are thought to be related to localized stress or strain at a point, while propagation of a fatigue crack is a function of the crack tip parameters such as crack shape, stress state, and stress intensity factor. During a test there is no clear transition between initiation and propagation. The mechanisms of initiation and propagation are quite different and modeling them separately produces a higher degree of accuracy, but then the question that continually arises is 'what is a crack?' The total life prediction in a fracture mechanics model presently hinges on the assumption of an initial crack length, and this length can significantly affect the total life prediction. The size of the initial crack is generally taken to be in the range of 0.01 in. to 0.2 in. Several researchers have used various techniques to determine the beginning of the crack propagation stage. Barhorst showed the relationship between dynamic stiffness changes and crack propagation. Acoustic emissions, which are stress waves produced by the sudden movement of stressed materials, have also been successfully used to monitor the growth of cracks in tensile and fatigue specimens. The purpose of this research is to determine whether acoustic emissions can be used to define the beginning of crack propagation in a gear using a single-tooth bending fatigue test.

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

NASA Technical Reports Server (NTRS)

Murri, Gretchen B.; OBrien, T. Kevin; Rousseau, Carl Q.

1997-01-01

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

Fatigue Life Methodology for Tapered Composite Flexbeam Laminates

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

Sequential segmental neuromuscular stimulation: an effective approach to enhance fatigue resistance.

PubMed

Zonnevijlle, E D; Somia, N N; Stremel, R W; Maldonado, C J; Werker, P M; Kon, M; Barker, J H

2000-02-01

Electrical stimulation of skeletal muscle flaps is used clinically in applications that require contraction of muscle and force generation at the recipient site, for example, to assist a failing myocardium (cardiomyoplasty) or to reestablish urinary or fecal continence as a neo-sphincter (dynamic graciloplasty). A major problem in these applications (muscle fatigue) results from the nonphysiologic manner in which most of the fibers within the muscle are recruited in a single burst-like contraction. To circumvent this problem, current protocols call for the muscle to be put through a rigorous training regimen to transform it from a fatigue-prone to a fatigue-resistant state. This process takes several weeks during which, aside from becoming fatigue-resistant, the muscle loses power and contraction speed. This study tested the feasibility of electrically stimulating a muscle flap in a more physiologic way; namely, by stimulating different anatomical parts of the muscle sequentially rather than the entire muscle all at once. Sequential segmental neuromuscular stimulation (SSNS) allows parts of the muscle to rest while other parts are contracting. In a paired designed study in dogs (n = 7), the effects of SSNS on muscle fatigability and muscle blood perfusion in gracilis muscles were compared with conventional stimulation: SSNS on one side and whole muscle stimulation on the other. In SSNS, electrodes were implanted in the muscles in such a way that four separate segments of each muscle could be stimulated separately. Then, each segment was stimulated so that part of the muscle was always contracted while part was always resting. This type of stimulation permitted sequential yet continuous force generation. Muscles in both groups maintained an equal amount of continuous force. In SSNS muscles, separate segments were stimulated so that the duty cycle for any one segment was 25, 50, 75, or 100 percent, thus varying the amount of work and rest that any segment experienced at any one time. With duty cycles of 25, 50, and 75 percent, SSNS produced significantly (p < 0.01) enhanced resistance to fatigue. In addition, muscle perfusion was significantly (p < 0.01) increased in these sequentially stimulated muscles compared with the controls receiving whole muscle stimulation. It was concluded that SSNS reduces muscle fatigue and enhances muscle blood flow during stimulation. These findings suggest that using SSNS in clinical myoplasty procedures could obviate the need for prolonged training protocols and minimize problems associated with muscle training.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

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 treatmentsmore » 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.« less

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

NASA Technical Reports Server (NTRS)

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

1985-01-01

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

The influence of matrix microstructure

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; Aken, D. C.

1993-11-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and artificially aged 2219/TiC/15p and unreinforced 2219 Al were investigated utilizing plastic strain-controlled and stress-controlled testing. The cyclic response of both the reinforced and un-reinforced materials was similar for all plastic strain amplitudes tested except that the saturation stress level for the composite was always greater than that of the unreinforced material. The cyclic response of the naturally aged materials exhibited cyclic hardening and, in some cases, cyclic softening, while the cyclic response for the artificially aged materials showed no evidence of either cyclic hardening or softening. The higher ductility of the unreinforced material made it more resistant to fatigue failure at high strains, and thus, at a given plastic strain, it had longer fatigue life. It should be noted that the tensile ductilities of the 2219/TiC/15p were significantly higher than those previously reported for 2XXX-series composites. During stress-controlled test-ing at stresses below 220 MPa, the presence of TiC particles lead to an improvement in fatigue life. Above 220 MPa, no influence of TiC reinforcement on fatigue life could be detected. In both the composite and unreinforced materials, the low-cycle and high-cycle fatigue lives were found to be virtually independent of matrix microstructure.

The reliability and validity of fatigue measures during short-duration maximal-intensity intermittent cycling.

PubMed

Glaister, Mark; Stone, Michael H; Stewart, Andrew M; Hughes, Michael; Moir, Gavin L

2004-08-01

The purpose of the present study was to assess the reliability and validity of fatigue measures, as derived from 4 separate formulae, during tests of repeat sprint ability. On separate days over a 3-week period, 2 groups of 7 recreationally active men completed 6 trials of 1 of 2 maximal (20 x 5 seconds) intermittent cycling tests with contrasting recovery periods (10 or 30 seconds). All trials were conducted on a friction-braked cycle ergometer, and fatigue scores were derived from measures of mean power output for each sprint. Apart from formula 1, which calculated fatigue from the percentage difference in mean power output between the first and last sprint, all remaining formulae produced fatigue scores that showed a reasonably good level of test-retest reliability in both intermittent test protocols (intraclass correlation range: 0.78-0.86; 95% likely range of true values: 0.54-0.97). Although between-protocol differences in the magnitude of the fatigue scores suggested good construct validity, within-protocol differences highlighted limitations with each formula. Overall, the results support the use of the percentage decrement score as the most valid and reliable measure of fatigue during brief maximal intermittent work.

Prediction of the Creep-Fatigue Lifetime of Alloy 617: An Application of Non-destructive Evaluation and Information Integration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vivek Agarwal; Richard Wright; Timothy Roney

A relatively simple method using the nominal constant average stress information and the creep rupture model is developed to predict the creep-fatigue lifetime of Alloy 617, in terms of time to rupture. The nominal constant average stress is computed using the stress relaxation curve. The predicted time to rupture can be converted to number of cycles to failure using the strain range, the strain rate during each cycle, and the hold time information. The predicted creep-fatigue lifetime is validated against the experimental measurements of the creep-fatigue lifetime collected using conventional laboratory creep-fatigue tests. High temperature creep-fatigue tests of Alloy 617more » were conducted in air at 950°C with a tensile hold period of up to 1800s in a cycle at total strain ranges of 0.3% and 0.6%. It was observed that the proposed method is conservative in that the predicted lifetime is less than the experimentally determined values. The approach would be relevant to calculate the remaining useful life to a component like a steam generator that might fail by the creep-fatigue mechanism.« less

TTK Chitra tilting disc heart valve model TC2: An assessment of fatigue life and durability.

PubMed

Subhash, N N; Rajeev, Adathala; Sujesh, Sreedharan; Muraleedharan, C V

2017-08-01

Average age group of heart valve replacement in India and most of the Third World countries is below 30 years. Hence, the valve for such patients need to be designed to have a service life of 50 years or more which corresponds to 2000 million cycles of operation. The purpose of this study was to assess the structural performance of the TTK Chitra tilting disc heart valve model TC2 and thereby address its durability. The TC2 model tilting disc heart valves were assessed to evaluate the risks connected with potential structural failure modes. To be more specific, the studies covered the finite element analysis-based fatigue life prediction and accelerated durability testing of the tilting disc heart valves for nine different valve sizes. First, finite element analysis-based fatigue life prediction showed that all nine valve sizes were in the infinite life region. Second, accelerated durability test showed that all nine valve sizes remained functional for 400 million cycles under experimental conditions. The study ensures the continued function of TC2 model tilting disc heart valves over duration in excess of 50 years. The results imply that the TC2 model valve designs are structurally safe, reliable and durable.

Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

DOE PAGES

Wu, Wei; An, Ke; Liaw, Peter K.

2014-12-23

In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustionmore » of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. Furthermore, the deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.« less

Muscle Performance Investigated With a Novel Smart Compression Garment Based on Pressure Sensor Force Myography and Its Validation Against EMG.

PubMed

Belbasis, Aaron; Fuss, Franz Konstantin

2018-01-01

Muscle activity and fatigue performance parameters were obtained and compared between both a smart compression garment and the gold-standard, a surface electromyography (EMG) system during high-speed cycling in seven participants. The smart compression garment, based on force myography (FMG), comprised of integrated pressure sensors that were sandwiched between skin and garment, located on five thigh muscles. The muscle activity was assessed by means of crank cycle diagrams (polar plots) that displayed the muscle activity relative to the crank cycle. The fatigue was assessed by means of the median frequency of the power spectrum of the EMG signal; the fractal dimension (FD) of the EMG signal; and the FD of the pressure signal. The smart compression garment returned performance parameters (muscle activity and fatigue) comparable to the surface EMG. The major differences were that the EMG measured the electrical activity, whereas the pressure sensor measured the mechanical activity. As such, there was a phase shift between electrical and mechanical signals, with the electrical signals preceding the mechanical counterparts in most cases. This is specifically pronounced in high-speed cycling. The fatigue trend over the duration of the cycling exercise was clearly reflected in the fatigue parameters (FDs and median frequency) obtained from pressure and EMG signals. The fatigue parameter of the pressure signal (FD) showed a higher time dependency ( R 2 = 0.84) compared to the EMG signal. This reflects that the pressure signal puts more emphasis on the fatigue as a function of time rather than on the origin of fatigue (e.g., peripheral or central fatigue). In light of the high-speed activity results, caution should be exerted when using data obtained from EMG for biomechanical models. In contrast to EMG data, activity data obtained from FMG are considered more appropriate and accurate as an input for biomechanical modeling as they truly reflect the mechanical muscle activity. In summary, the smart compression garment based on FMG is a valid alternative to EMG-garments and provides more accurate results at high-speed activity (avoiding the electro-mechanical delay), as well as clearly measures the progress of muscle fatigue over time.

Muscle Performance Investigated With a Novel Smart Compression Garment Based on Pressure Sensor Force Myography and Its Validation Against EMG

PubMed Central

Belbasis, Aaron; Fuss, Franz Konstantin

2018-01-01

Muscle activity and fatigue performance parameters were obtained and compared between both a smart compression garment and the gold-standard, a surface electromyography (EMG) system during high-speed cycling in seven participants. The smart compression garment, based on force myography (FMG), comprised of integrated pressure sensors that were sandwiched between skin and garment, located on five thigh muscles. The muscle activity was assessed by means of crank cycle diagrams (polar plots) that displayed the muscle activity relative to the crank cycle. The fatigue was assessed by means of the median frequency of the power spectrum of the EMG signal; the fractal dimension (FD) of the EMG signal; and the FD of the pressure signal. The smart compression garment returned performance parameters (muscle activity and fatigue) comparable to the surface EMG. The major differences were that the EMG measured the electrical activity, whereas the pressure sensor measured the mechanical activity. As such, there was a phase shift between electrical and mechanical signals, with the electrical signals preceding the mechanical counterparts in most cases. This is specifically pronounced in high-speed cycling. The fatigue trend over the duration of the cycling exercise was clearly reflected in the fatigue parameters (FDs and median frequency) obtained from pressure and EMG signals. The fatigue parameter of the pressure signal (FD) showed a higher time dependency (R2 = 0.84) compared to the EMG signal. This reflects that the pressure signal puts more emphasis on the fatigue as a function of time rather than on the origin of fatigue (e.g., peripheral or central fatigue). In light of the high-speed activity results, caution should be exerted when using data obtained from EMG for biomechanical models. In contrast to EMG data, activity data obtained from FMG are considered more appropriate and accurate as an input for biomechanical modeling as they truly reflect the mechanical muscle activity. In summary, the smart compression garment based on FMG is a valid alternative to EMG-garments and provides more accurate results at high-speed activity (avoiding the electro-mechanical delay), as well as clearly measures the progress of muscle fatigue over time. PMID:29725306

Statistical optimisation techniques in fatigue signal editing problem

NASA Astrophysics Data System (ADS)

Nopiah, Z. M.; Osman, M. H.; Baharin, N.; Abdullah, S.

2015-02-01

Success in fatigue signal editing is determined by the level of length reduction without compromising statistical constraints. A great reduction rate can be achieved by removing small amplitude cycles from the recorded signal. The long recorded signal sometimes renders the cycle-to-cycle editing process daunting. This has encouraged researchers to focus on the segment-based approach. This paper discusses joint application of the Running Damage Extraction (RDE) technique and single constrained Genetic Algorithm (GA) in fatigue signal editing optimisation.. In the first section, the RDE technique is used to restructure and summarise the fatigue strain. This technique combines the overlapping window and fatigue strain-life models. It is designed to identify and isolate the fatigue events that exist in the variable amplitude strain data into different segments whereby the retention of statistical parameters and the vibration energy are considered. In the second section, the fatigue data editing problem is formulated as a constrained single optimisation problem that can be solved using GA method. The GA produces the shortest edited fatigue signal by selecting appropriate segments from a pool of labelling segments. Challenges arise due to constraints on the segment selection by deviation level over three signal properties, namely cumulative fatigue damage, root mean square and kurtosis values. Experimental results over several case studies show that the idea of solving fatigue signal editing within a framework of optimisation is effective and automatic, and that the GA is robust for constrained segment selection.

Statistical optimisation techniques in fatigue signal editing problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nopiah, Z. M.; Osman, M. H.; Baharin, N.

Success in fatigue signal editing is determined by the level of length reduction without compromising statistical constraints. A great reduction rate can be achieved by removing small amplitude cycles from the recorded signal. The long recorded signal sometimes renders the cycle-to-cycle editing process daunting. This has encouraged researchers to focus on the segment-based approach. This paper discusses joint application of the Running Damage Extraction (RDE) technique and single constrained Genetic Algorithm (GA) in fatigue signal editing optimisation.. In the first section, the RDE technique is used to restructure and summarise the fatigue strain. This technique combines the overlapping window andmore » fatigue strain-life models. It is designed to identify and isolate the fatigue events that exist in the variable amplitude strain data into different segments whereby the retention of statistical parameters and the vibration energy are considered. In the second section, the fatigue data editing problem is formulated as a constrained single optimisation problem that can be solved using GA method. The GA produces the shortest edited fatigue signal by selecting appropriate segments from a pool of labelling segments. Challenges arise due to constraints on the segment selection by deviation level over three signal properties, namely cumulative fatigue damage, root mean square and kurtosis values. Experimental results over several case studies show that the idea of solving fatigue signal editing within a framework of optimisation is effective and automatic, and that the GA is robust for constrained segment selection.« less

Evaluation of the Effect of Surface Finish on High-Cycle Fatigue of SLM-IN718

NASA Technical Reports Server (NTRS)

Lambert, D. M.

2016-01-01

The surface finish of parts produced by additive manufacturing processes is much rougher than the surface finish generated by machining processes, and a rougher surface can reduce the fatigue strength of a part. This paper discusses an effort to quantify that reduction of strength in high-cycle fatigue for selective laser melt (SLM) coupons. A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the SLM process. This factor is the percentage reduction from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition at the same fatigue life. Specimens were provided by a number of vendors, free to use their "best practice"; only one heat treat condition was considered; and several test temperatures were characterized, including room temperature, 800F, 1000F, and 1200F. The 1000F data had a large variance, and was omitted from consideration in this document. A first method used linear approximations extracted from the graphs, and only where data was available for both. A recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness no more than 4 micro-inches/inch) was established at approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce a similar life in the as-built surface condition. In this first evaluation, the knockdown factor did not appear to be a function of temperature. A second approach, the "KP method", incorporated the surface finish measure into a new parameter termed the pseudo-stress intensity factor, Kp, which was formulated to be similar to the fracture mechanics stress intensity factor. Using Kp, the variance seemed to be reduced across all sources, and knockdown factors were estimated using Kp over the range where data occurred. A plot of the results suggests that the knockdown factor is a function of temperature, and that for low lives the knockdown might be lower than the knockdown observed above about one million cycles, where it tended to stabilize. This was not universal for all temperatures tested. The higher temperature tests are thought to be influenced by the test temperature, which perhaps continued the aging process. Further evaluation of the method is suggested.

High cycle fatigue crack modeling and analysis for deck truss flooring connection details : appendices.

DOT National Transportation Integrated Search

1997-07-01

The appendix belongs to "High cycle fatigue crack modeling and analysis for deck truss flooring connection details : final report". : The Oregon Department of Transportation is responsible for many steel deck truss bridges containing connection detai...

Fatigue Damage and Lifetime of SiC/SiC Ceramic-Matrix Composite under Cyclic Loading at Elevated Temperatures

PubMed Central

Li, Longbiao

2017-01-01

In this paper, the fatigue damage and lifetime of 2D SiC/SiC ceramic-matrix composites (CMCs) under cyclic fatigue loading at 750, 1000, 1100, 1200 and 1300 °C in air and in steam atmosphere have been investigated. The damage evolution versus applied cycles of 2D SiC/SiC composites were analyzed using fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and interface shear stress. The presence of steam accelerated the damage development inside of SiC/SiC composites, which increased the increasing rate of the fatigue hysteresis dissipated energy and the fatigue peak strain, and the decreasing rate of the fatigue hysteresis modulus and the interface shear stress. The fatigue life stress-cycle (S-N) curves and fatigue limit stresses of 2D SiC/SiC composites at different temperatures in air and in steam condition have been predicted. The fatigue limit stresses approach 67%, 28%, 39% 17% and 28% tensile strength at 750, 1000, 1100, 1200 and 1300 °C in air, and 49%, 10%, 9% and 19% tensile strength at 750, 1000, 1200 and 1300 °C in steam conditions, respectively. PMID:28772736

Data-Driven Mechanistic Modeling of Influence of Microstructure on High-Cycle Fatigue Life of Nickel Titanium

NASA Astrophysics Data System (ADS)

Kafka, Orion L.; Yu, Cheng; Shakoor, Modesar; Liu, Zeliang; Wagner, Gregory J.; Liu, Wing Kam

2018-04-01

A data-driven mechanistic modeling technique is applied to a system representative of a broken-up inclusion ("stringer") within drawn nickel-titanium wire or tube, e.g., as used for arterial stents. The approach uses a decomposition of the problem into a training stage and a prediction stage. It is applied to compute the fatigue crack incubation life of a microstructure of interest under high-cycle fatigue. A parametric study of a matrix-inclusion-void microstructure is conducted. The results indicate that, within the range studied, a larger void between halves of the inclusion increases fatigue life, while larger inclusion diameter reduces fatigue life.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Sokolov, Mikhail A; Sham, Sam

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

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

NASA Astrophysics Data System (ADS)

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

2013-01-01

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

Probabilistic Fatigue Damage Program (FATIG)

NASA Technical Reports Server (NTRS)

Michalopoulos, Constantine

2012-01-01

FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading

PubMed Central

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-01-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress–strain responses for each cycle, and the hysteresis stress–strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given. PMID:26937465

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading.

PubMed

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-03-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress-strain responses for each cycle, and the hysteresis stress-strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given.

Tensile and compressive failure modes of laminated composites loaded by fatigue with different mean stress

NASA Technical Reports Server (NTRS)

Rotem, Assa

1990-01-01

Laminated composite materials tend to fail differently under tensile or compressive load. Under tension, the material accumulates cracks and fiber fractures, while under compression, the material delaminates and buckles. Tensile-compressive fatigue may cause either of these failure modes depending on the specific damage occurring in the laminate. This damage depends on the stress ratio of the fatigue loading. Analysis of the fatigue behavior of the composite laminate under tension-tension, compression-compression, and tension-compression had led to the development of a fatigue envelope presentation of the failure behavior. This envelope indicates the specific failure mode for any stress ratio and number of loading cycles. The construction of the fatigue envelope is based on the applied stress-cycles to failure (S-N) curves of both tensile-tensile and compressive-compressive fatigue. Test results are presented to verify the theoretical analysis.

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

PubMed Central

Li, Longbiao

2015-01-01

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.

Corrosion fatigue behaviors of two biomedical Mg alloys - AZ91D and WE43 - In simulated body fluid.

PubMed

Gu, X N; Zhou, W R; Zheng, Y F; Cheng, Y; Wei, S C; Zhong, S P; Xi, T F; Chen, L J

2010-12-01

Magnesium alloys have been recently developed as biodegradable implant materials, yet there has been no study concerning their corrosion fatigue properties under cyclic loading. In this study the die-cast AZ91D (A for aluminum 9%, Z for zinc 1% and D for a fourth phase) and extruded WE43 (W for yttrium 4%, E for rare earth mischmetal 3%) alloys were chosen to evaluate their fatigue and corrosion fatigue behaviors in simulated body fluid (SBF). The die-cast AZ91D alloy indicated a fatigue limit of 50MPa at 10⁷ cycles in air compared to 20MPa at 10⁶ cycles tested in SBF at 37°C. A fatigue limit of 110MPa at 10⁷ cycles in air was observed for extruded WE43 alloy compared to 40MPa at 10⁷ cycles tested in SBF at 37°C. The fatigue cracks initiated from the micropores when tested in air and from corrosion pits when tested in SBF, respectively. The overload zone of the extruded WE43 alloy exhibited a ductile fracture mode with deep dimples, in comparison to a brittle fracture mode for the die-cast AZ91D. The corrosion rate of the two experimental alloys increased under cyclic loading compared to that in the static immersion test. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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

NASA Technical Reports Server (NTRS)

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.

Helicopter Fatigue. A Review of Current Requirements and Substantiation Procedures

DTIC Science & Technology

1979-01-01

which the applications differ between contractors based cn their individual experience. Load Application: The ideal method of measuring flight loads would... method is different for the parts mainly dimensioned by high cycle fatigue (rotors and gearboxes) and for those subjected to low cycle fatigue (e.g...into damage per hour. Z.. A 58 2.3. Calculation of the service life Two methods are available, both with advantages and drawbacks. They only differ by

Comparative thermal fatigue resistances of twenty-six nickel and cobalt base alloys

NASA Technical Reports Server (NTRS)

Bizon, P. T.; Spera, D. A.

1975-01-01

Thermal fatigue resistances were determined from fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials with directional solidification and surface protection of definite benefit. The alloy-coating combination with the highest thermal fatigue resistance was directionally solidified NASA TAZ-8A with an RT-XP coating. It oxidation resistance was excellent, showing almost no weight change after 15 000 fluidized bed cycles.

A lightweight ambient air-cooling unit for use in hazardous environments.

PubMed

Chen, Y T; Constable, S H; Bomalaski, S H

1997-01-01

Recent research demonstrated (a) the effectiveness of intermittent conditioned air cooling during rest breaks to significantly reduce cumulative heat storage and (b) that longer work sessions were possible for individuals wearing chemical defense ensembles. To further advance this concept, a strategy for implementing continuous air cooling was conceived; ambient air cooling was added during work cycles and conditioned air cooling was delivered during rest periods. A compact battery-powered beltpack cooling unit (3.9 kg) designed and made at the U.S. Air Force Armstrong Laboratory was used to deliver 5.7 L/sec filtered ambient air during work cycles: 4.7 L/sec to the body and 1 L/sec to the face. Five experimental cycles were conducted in a thermally controlled chamber under warm conditions (32 degrees C, 40% relative humidity) with (1) no cooling-intermittent work, (2) intermittent cooling, (3) continuous cooling during intermittent exercise, and (4) no cooling-continuous work and (5) ambient air cooling during continuous exercise. Intermittent, conditioned, and continuous air cooling resulted in significant reductions in rectal temperature, mean skin temperature, and heart rate as compared with the no-cooling trials. The continuous air-cooling trial significantly improved thermal comfort and sweat evaporation. Results suggest that ambient air delivered during work cycles by a lightweight portable unit (in conjunction with conditioned air delivered during rest periods), can definitely improve personal comfort, reduce skin temperature, and decrease the cumulative fatigue common to repeated work/rest cycles in selected military and industrial applications in which individuals work in chemical defense ensembles.

High-cycle fatigue characterization of titanium 5Al-2.5Sn alloy

NASA Technical Reports Server (NTRS)

Mahfuz, H.; Xin, Yu T.; Jeelani, S.

1993-01-01

High-cycle fatigue behavior of titanium 5Al 2.5Sn alloy at room temperature has been studied. S-N curve characterization is performed at different stress ratios ranging from 0 to 0.9 on a subsized fatigue specimen. Both two-stress and three-stress level tests are conducted at different stress ratios to study the cumulative fatigue damage. Life prediction techniques of linear damage rule, double linear damage rule and damage curve approaches are applied, and results are compared with the experimental data. The agreement between prediction and experiment is found to be excellent.

Influence of localized deformation on A-286 austenitic stainless steel stress corrosion cracking in PWR primary water

NASA Astrophysics Data System (ADS)

Fournier, L.; Savoie, M.; Delafosse, D.

2007-06-01

The low cycle fatigue (LCF) behaviour of precipitation-strengthened A-286 austenitic stainless steel was first investigated at room temperature under 0.2% plastic strain control. LCF led to hardening for the first 20 cycles and then to significant softening. LCF-induced dislocation microstructure was characterized using both bright and dark-field imaging techniques in transmission electron microscopy. Cycling softening was correlated with the formation of precipitate-free localized deformation bands. The effect of these precipitate-free localized deformation bands on A-286 stress corrosion cracking (SCC) behaviour in PWR primary water was then examined by means of constant extension rate tensile (CERT) tests at 320 °C and 360 °C. Comparative CERT tests were performed on companion specimens with similar yield stress but pre-fatigued to a few cycles (4-8) or between 125 and 200 cycles. Specimens pre-fatigued to a few cycles with no precipitate-free localized deformation bands exhibited little susceptibility to intergranular SCC (IGSCC). In contrast, the presence of precipitate-free localized deformation bands formed by pre-fatigue to between 125 and 200 cycles strongly promoted IGSCC. The interest of the approach used in this study is to provide insight into the role of localized deformation in irradiation assisted stress corrosion cracking.

High-temperature fatigue life of type 316 stainless steel containing irradiation induced helium

NASA Astrophysics Data System (ADS)

Grossbeck, M. L.; Liu, K. C.

Specimens of 20%-cold-worked AISI type 316 stainless steel were irradiated in the High Flux Isotope Reactor (HFIR) at 550°C to a maximum damage level of 15 dpa and a transmutation produced helium level of 820 at. ppm. Fully reversed strain controlled fatigue tests were performed in a vacuum at 550°C. No significant effect of the irradiation on low-cycle fatigue life was observed; however, the strain range of the 10 7 cycle endurance limit decreased from 0.35 to 0.30%. The relation between total strain range and number of cycles to failure was found to be ΔEt = 0.02 Nf-0.12+ Nf-0.6 for N f < 10 7 cycles.

Conditioning monitoring by microstructural evaluation of cumulative fatigue damage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuoka, C.; Nakagawa, Y.G.; Lance, J.J.

1996-12-01

The objective of this work is to evaluate the damage induced below and above the fatigue limit ({Delta}{sigma}{sub t} = 360 MPa) in pressure vessel steels, such as SA508. Fatigue damage was induced in samples taken from an SA508 steel plate by various loading histories in order to examine the influence of prior cyclic loading below the fatigue limit. Cell-to-cell misorientation differences were measured by the selected area diffraction (SAD) method. Surface cracking was also studied by the replication method. Small cracks were observed after precycling both below and above the fatigue limit. It was, however, found that fatigue testmore » bars had a longer lifetime after precycling below the fatigue limit, while precycling above the fatigue limit caused other specimens to fail even when subsequently cycled below the fatigue limit. Cell-to-cell misorientation usually increases with accumulation of fatigue damage, but it was found that the misorientations measured after precycling below the fatigue limit decreased again at the beginning of the subsequent cycling above the fatigue limit. It should be noted that the misorientation at failure was always about 4 to 5 deg, regardless of loading histories. Misorientation showed good correlation with the fatigue lifetime of the samples.« less

Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

NASA Technical Reports Server (NTRS)

Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

1976-01-01

During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The chamber liners were fabricated of copper or copper alloy and contained milled coolant channels. The chambers were completed by means of an electroformed nickel closeout. The oxidant/fuel ratio for the liquid oxygen and gaseous hydrogen propellants was 6.0. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The lives were much shorter than were predicted by an analytical structural analysis computer program used in conjunction with fatigue life data from isothermal test specimens, due to the uneven distribution of Zr in the chamber material.

Assessing Corrosion Damage and Corrosion Progression in Multistrand Anchor Systems in Use at Corps Projects

DTIC Science & Technology

2013-07-01

14  4.8  Corrosion fatigue ...particularly vulnerable. ERDC TR-13-3 15 4.8 Corrosion fatigue Fatigue that takes place in a corrosive environment can reduce the number of...cycles generally considered acceptable before fatigue and fatigue -related failure occur. ERDC TR-13-3 16 5 Historical Perspective: Post-Tensioned

Evaluation of Cyclic Behavior of Aircraft Turbine Disk Alloys

NASA Technical Reports Server (NTRS)

Shahani, V.; Popp, H. G.

1978-01-01

An evaluation of the cyclic behavior of three aircraft engine turbine disk materials was conducted to compare their relative crack initiation and crack propagation resistance. The disk alloys investigated were Inconel 718, hot isostatically pressed and forged powder metallurgy Rene '95, and as-hot-isostatically pressed Rene '95. The objective was to compare the hot isostatically pressed powder metallurgy alloy forms with conventionally processed superalloys as represented by Inconel 718. Cyclic behavior was evaluated at 650 C both under continuously cycling and a fifteen minute tensile hold time cycle to simulate engine conditions. Analysis of the test data were made to evaluate the strain range partitioning and energy exhaustion concepts for predicting hold time effects on low cycle fatigue.

High temperature, low-cycle fatigue of copper-base alloys in argon. Part 2: Zirconium-copper at 482, 538 and 593 C

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

Zirconium-copper (1/2 hard) was tested in argon over the temperature range from 482 to 593 C in an evaluation of short-term tensile and low-cycle fatigue behavior. The effect of strain rate on the tensile properties was evaluated at 538 C and in general it was found that the yield and ultimate strengths increased as the strain rate was increased from 0.0004 to 0.01/sec. Ductility was essentially insensitive to strain rate in the case of the zirconium-copper alloy. Strain-rate and hold-time effects on the low cycle fatigue behavior of zirconium-copper were evaluated in argon at 538 C. These effects were as expected in that decreased fatigue life was noted as the strain rate decreased and when hold times were introduced into the tension portion of the strain-cycle. Hold times in compression were much less detrimental than hold times in tension.

Fatigue Crack Growth Threshold Testing of Metallic Rotorcraft Materials

NASA Technical Reports Server (NTRS)

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.

High cycle fatigue in the transmission electron microscope

DOE PAGES

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; ...

2016-06-28

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

High cycle fatigue in the transmission electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

The onset and evolution of fatigue-induced abnormal grain growth in nanocrystalline Ni–Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furnish, T. A.; Mehta, A.; Van Campen, D.

Conventional structural metals suffer from fatigue-crack initiation through dislocation activity which forms persistent slip bands leading to notch-like extrusions and intrusions. Ultrafine-grained and nanocrystalline metals can potentially exhibit superior fatigue-crack initiation resistance by suppressing these cumulative dislocation activities. Prior studies on these metals have confirmed improved high-cycle fatigue performance. In the case of nano-grained metals, analyses of subsurface crack initiation sites have indicated that the crack nucleation is associated with abnormally large grains. But, these post-mortem analyses have led to only speculation about when abnormal grain growth occurs (e.g., during fatigue, after crack initiation, or during crack growth). In thismore » study, a recently developed synchrotron X-ray diffraction technique was used to detect the onset and progression of abnormal grain growth during stress-controlled fatigue loading. Our study provides the first direct evidence that the grain coarsening is cyclically induced and occurs well before final fatigue failure—our results indicate that the first half of the fatigue life was spent prior to the detectable onset of abnormal grain growth, while the second half was spent coarsening the nanocrystalline structure and cyclically deforming the abnormally large grains until crack initiation. Post-mortem fractography, coupled with cycle-dependent diffraction data, provides the first details regarding the kinetics of this abnormal grain growth process during high-cycle fatigue testing. Finally, precession electron diffraction images collected in a transmission electron microscope after the in situ fatigue experiment also confirm the X-ray evidence that the abnormally large grains contain substantial misorientation gradients and sub-grain boundaries.« less

The onset and evolution of fatigue-induced abnormal grain growth in nanocrystalline Ni–Fe

DOE PAGES

Furnish, T. A.; Mehta, A.; Van Campen, D.; ...

2016-10-11

Conventional structural metals suffer from fatigue-crack initiation through dislocation activity which forms persistent slip bands leading to notch-like extrusions and intrusions. Ultrafine-grained and nanocrystalline metals can potentially exhibit superior fatigue-crack initiation resistance by suppressing these cumulative dislocation activities. Prior studies on these metals have confirmed improved high-cycle fatigue performance. In the case of nano-grained metals, analyses of subsurface crack initiation sites have indicated that the crack nucleation is associated with abnormally large grains. But, these post-mortem analyses have led to only speculation about when abnormal grain growth occurs (e.g., during fatigue, after crack initiation, or during crack growth). In thismore » study, a recently developed synchrotron X-ray diffraction technique was used to detect the onset and progression of abnormal grain growth during stress-controlled fatigue loading. Our study provides the first direct evidence that the grain coarsening is cyclically induced and occurs well before final fatigue failure—our results indicate that the first half of the fatigue life was spent prior to the detectable onset of abnormal grain growth, while the second half was spent coarsening the nanocrystalline structure and cyclically deforming the abnormally large grains until crack initiation. Post-mortem fractography, coupled with cycle-dependent diffraction data, provides the first details regarding the kinetics of this abnormal grain growth process during high-cycle fatigue testing. Finally, precession electron diffraction images collected in a transmission electron microscope after the in situ fatigue experiment also confirm the X-ray evidence that the abnormally large grains contain substantial misorientation gradients and sub-grain boundaries.« less

The multiaxial fatigue response of cylindrical geometry under proportional loading subject to fluctuating tractions

NASA Astrophysics Data System (ADS)

Martinez, Rudy D.

A multiaxial fatigue model is proposed, as it would apply to cylindrical geometry in the form of industrial sized pressure vessels. The main focus of the multiaxial fatigue model will be based on using energy methods with the loading states confined to fluctuating tractions under proportional loading. The proposed fatigue model is an effort to support and enhance existing fatigue life predicting methods for pressure vessel design, beyond the ASME Boiler and Pressure Vessel codes, ASME Section VIII Division 2 and 3, which is currently used in industrial engineering practice for pressure vessel design. Both uniaxial and biaxial low alloy pearlittic-ferritic steel cylindrical cyclic test data are utilized to substantiate the proposed fatigue model. Approximate material hardening and softening aspects from applied load cycling states and the Bauschinger effect are accounted for by adjusting strain control generated hysteresis loops and the cyclic stress strain curve. The proposed fatigue energy model and the current ASME fatigue model are then compared with regards to the accuracy of predicting fatigue life cycle consistencies.

High temperature low-cycle fatigue mechanisms in single crystals of nickel-based superalloy Mar-M 200

NASA Technical Reports Server (NTRS)

Milligan, W. W.; Jayaraman, N.

1984-01-01

Twenty three high temperature low-cycle fatigue tests were conducted on single crystals of the nickel-based superalloy Mar-M 200. Tests were conducted at 760 and 870 C. SEM fractography and transmission electron microscopy were used to determine mechanisms responsible for the observed orientation dependent fatigue behavior. It has been concluded that the plastic characteristics of the alloy lead to orientation-dependent strain hardening and fatigue lives at 760 C. At 870 C, the elastic characteristics of the alloy dominated the behavior, even though the plastic strain ranges were about the same as they were at 760 C. This led to orientation-dependent fatigue lives, but the trends were not the same as they were at 760 C.

Design solutions for the solar cell interconnect fatigue fracture problem

NASA Technical Reports Server (NTRS)

Mon, G. R.; Ross, R. G., Jr.

1982-01-01

Mechanical fatigue of solar cell interconnects is a major failure mechanism in photovoltaic arrays. A comprehensive approach to the reliability design of interconnects, together with extensive design data for the fatigue properties of copper interconnects, has been published. This paper extends the previous work, developing failure prediction (fatigue) data for additional interconnect material choices, including aluminum and a variety of copper-Invar and copper-steel claddings. An improved global fatigue function is used to model the probability-of-failure statistics of each material as a function of level and number of cycles of applied strain. Life-cycle economic analyses are used to evaluate the relative merits of each material choce. The copper-Invar clad composites demonstrate superior performance over pure copper. Aluminum results are disappointing.

75 FR 27972 - Airworthiness Directives; Pratt & Whitney JT8D-9, -9A, -11, -15, -17, and -17R Turbofan Engines

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-19

... cycles-in-service (CIS) since the last total fan blade overhaul was performed. This proposed AD results from reports of failed fan blades. We are proposing this AD to prevent high-cycle fatigue cracking at...-cycle fatigue cracking at the blade root, which could result in uncontained failures of first stage fan...

Effects of environment and frequency on the fatigue behavior of the spallation neutron source (SNS) target container material - 316 LN stainless steel

NASA Astrophysics Data System (ADS)

Tian, Hongbo

As the candidate target container material of the new Spallation Neutron Source (SNS) being designed and constructed at the Oak Ridge National Laboratory (ORNL), Type 316 low-carbon nitrogen-added (LN) stainless steel (SS) will operate in an aggressive environment, subjected to intense fluxes of high-energy protons and neutrons while exposed to liquid mercury. The current project is oriented toward materials studies regarding the effects of test environment and frequency on the fatigue behavior of 316 LN SS. In order to study the structural applications of this material and improve the fundamental understanding of the fatigue damage mechanisms, fatigue tests were performed in air and mercury environments at various frequencies and R ratios (R = sigma min/sigmamax, sigmamin and sigmamax are the applied minimum and maximum stresses, respectively). Fatigue data were developed for the structural design and engineering applications of this material. Specifically, high-cycle fatigue tests, fatigue crack-propagation tests, and ultrahigh cycle fatigue tests up to 10 9 cycles were conducted in air and mercury with test frequencies from 10 Hz to 700 Hz. Microstructure characterizations were performed using optical microscopy (OM), scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). It was found that mercury doesn't seem to have a large impact on the crack-initiation behavior of 316 LN SS. However, the crack-propagation mechanisms in air and mercury are different in some test conditions. Transgranular cracks seem to be the main mechanism in air, and intergranular in mercury. A significant specimen self-heating effect was found during high-cycle faituge. Theoretical calculation was performed to predict temperature responses of the material subjected to cyclic deformation. The predicted cyclic temperature evolution seems to be in good agreement with the experimental results.

Accelerated Aging Experiments for Prognostics of Damage Growth in Composite Materials

DTIC Science & Technology

2011-09-01

possible resource to collect such data is an accelerated aging platform. To that end this paper describes a fatigue cycling experiment with the goal to...possible resource to collect such data is an accelerated aging platform. To that end this paper describes a fatigue cycling experiment with the goal to...suffer from two damage types: matrix micro-cracks and inter- laminar delamination. When subject to fatigue loading matrix micro-cracks develop in the

Crack Detection Using Combinations of Acoustic Emission and Guided Wave Signals from Bonded Piezoelectric Transducers

DTIC Science & Technology

2011-09-01

and bond integrity. Lastly, the PZT transducers are also utilized to track the lower frequency mechanical strains created during fatigue loading...face of the coupon and on either side of the gage section. Each coupon undergoes cyclic tensile loading to initiate and grow fatigue cracks. At...various intervals, the fatigue cycling is paused and the coupon is visually inspected for crack initiation and growth. While the cycling is paused

Evaluation of fatigue crack behavior in electron beam irradiated polyethylene pipes

NASA Astrophysics Data System (ADS)

Pokharel, Pashupati; Jian, Wei; Choi, Sunwoong

2016-09-01

A cracked round bar (CRB) fatigue test was employed to determine the slow crack growth (SCG) behavior of samples from high density polyethylene (HDPE) pipes using PE4710 resin. The structure property relationships of fatigue failure of polyethylene CRB specimens which have undergone various degree of electron beam (EB) irradiation were investigated by observing fatigue failure strength and the corresponding fracture surface morphology. Tensile test of these HDPE specimens showed improvements in modulus and yield strength while the failure strain decreased with increasing EB irradiation. The CRB fatigue test of HDPE pipe showed remarkable effect of EB irradiation on number of cycles to failure. The slopes of the stress-cycles to failure curve were similar for 0-100 kGy; however, significantly higher slope was observed for 500 kGy EB irradiated pipe. Also, the cycle to fatigue failure was seen to decrease as with EB irradiation in the high stress range, ∆σ=(16 MPa to 10.8 MPa); however, 500 kGy EB irradiated samples showed longer cycles to failure than the un-irradiated specimens at the stress range below 9.9 MPa and the corresponding initial stress intensity factor (∆KI,0)=0.712 MPa m1/2. The fracture surface morphology indicated that the cross-linked network in 500 kGy EB irradiated PE pipe can endure low dynamic load more effectively than the parent pipe.

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

NASA Technical Reports Server (NTRS)

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.

The influence of loading frequency on the high-temperature fatigue behavior of a Nicalon-fabric-reinforced polymer-derived ceramic-matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vanswijgenhoven, E.; Holmes, J.; Wevers, M.

Fiber-reinforced ceramic-matrix composites are under development for high-temperature structural applications. These applications involve fatigue loading under a wide range of frequencies. To date, high-temperature fatigue experiments have typically been performed at loading frequencies of 10 Hz or lower. At higher frequencies, a strong effect of loading frequency on fatigue life has been demonstrated for certain CMC`s tested at room temperature. The fatigue life of CMC`s with weak fiber-matrix interfaces typically decreases as the loading frequency increases. This decrease is attributed to frictional heating and frequency dependent interface and fiber damage. More recently, it has been shown that the room temperaturemore » fatigue life of a Nicalon-fabric-reinforced composite with a strong interface (SYLRAMIC{trademark}) appears to be independent of loading frequency. The high-temperature low-frequency fatigue behavior of the SYLRAMIC composite has also been investigated. For a fatigue peak stress {sigma}{sub peak} above a proportional limit stress of 70 MPa, the number of cycles to failure N{sub f} decreased with an increase in {sigma}{sub peak}. The material endured more than 10{sup 6} cycles for {sigma}{sub peak} below 70 MPa. In this paper, the influence of loading frequency on the high-temperature fatigue behavior of the SYLRAMIC composite is reported. It will be shown that the fatigue limit is unaffected by the loading frequency, that the number of fatigue cycles to failure N{sub f} increases with an increase in frequency, and that the time to failure t{sub f} decreases with an increase in frequency.« less

Modified Spectral Fatigue Methods for S-N Curves With MIL-HDBK-5J Coefficients

NASA Technical Reports Server (NTRS)

Irvine, Tom; Larsen, Curtis

2016-01-01

The rainflow method is used for counting fatigue cycles from a stress response time history, where the fatigue cycles are stress-reversals. The rainflow method allows the application of Palmgren-Miner's rule in order to assess the fatigue life of a structure subject to complex loading. The fatigue damage may also be calculated from a stress response power spectral density (PSD) using the semi-empirical Dirlik, Single Moment, Zhao-Baker and other spectral methods. These methods effectively assume that the PSD has a corresponding time history which is stationary with a normal distribution. This paper shows how the probability density function for rainflow stress cycles can be extracted from each of the spectral methods. This extraction allows for the application of the MIL-HDBK-5J fatigue coefficients in the cumulative damage summation. A numerical example is given in this paper for the stress response of a beam undergoing random base excitation, where the excitation is applied separately by a time history and by its corresponding PSD. The fatigue calculation is performed in the time domain, as well as in the frequency domain via the modified spectral methods. The result comparison shows that the modified spectral methods give comparable results to the time domain rainflow counting method.

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

NASA Technical Reports Server (NTRS)

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

2007-01-01

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

Matrix Fatigue Cracking Mechanisms of Alpha(2) TMC for Hypersonic Applications

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Gayda, John

1994-01-01

The objective of this work was to understand matrix cracking mechanisms in a unidirectional alpha(sub 2) TMC in possible hypersonic applications. A (0)(sub 8) SCS-6/Ti-24Al-11Nb (at. percent) TMC was first subjected to a variety of simple isothermal and nonisothermal fatigue cycles to evaluate the damage mechanisms in simple conditions. A modified ascent mission cycle test was then performed to evaluate the combined effects of loading modes. This cycle mixes mechanical cycling at 150 and 483 C, sustained loads, and a slow thermal cycle to 815 C. At low cyclic stresses and strains more common in hypersonic applications, environment-assisted surface cracking limited fatigue resistance. This damage mechanism was most acute for out-of-phase nonisothermal cycles having extended cycle periods and the ascent mission cycle. A simple linear fraction damage model was employed to help understand this damage mechanism. Time-dependent environmental damage was found to strongly influence out-of-phase and mission life, with mechanical cycling damage due to the combination of external loading and CTE mismatch stresses playing a smaller role. The mechanical cycling and sustained loads in the mission cycle also had a smaller role.

Effect of fabrication pressure on the fatigue performance of Cemex XL acrylic bone cement.

PubMed

Lewis, Gladius; Janna, S I

2004-01-01

During a cemented arthroplasty, the prepared polymerizing dough of acrylic bone cement is subjected to pressurization in a number of ways; first, during delivery into the freshly prepared bone bed, second, during packing in that bed (either digitally or with the aid of a mechanical device), and, third, during the insertion of the prosthesis. Only a few studies have reported on the influence of the level of pressurization experienced during these events (which, depending on the cementing technique used, has been put at between 8 and 273 kPa) on various properties of the cement. That was the focus of the present study, in which the fully reversed tension-compression (+/-15 MPa; 5 Hz) fatigue lives (expressed as number of cycles to fracture, N(f)) of rectangular cross-sectioned "dog-bone" specimens (Type V, per ASTM D 638) fabricated from Cemex XL cement, at pressure applied continuously to the cement dough during curing in the specimen mold, p=75,150, and 300 kPa, were determined. The N(f) results were analyzed using the linearized transformation of the three-parameter Weibull relationship to obtain estimates of the Weibull mean, N(WM), which was taken to be the index of fatigue performance of the specimen set. Over the range of p studied, N(WM) increased as p increased (for example, from 329,118 cycles when p was 75 kPa to 388,496 cycles when p was 300 kPa); however, the increase was not significant over any pair of p increment steps (Mann-Whitney U-test; alpha<0.05).

Reliable high-power diode lasers: thermo-mechanical fatigue aspects

NASA Astrophysics Data System (ADS)

Klumel, Genady; Gridish, Yaakov; Szafranek, Igor; Karni, Yoram

2006-02-01

High power water-cooled diode lasers are finding increasing demand in biomedical, cosmetic and industrial applications, where repetitive cw (continuous wave) and pulsed cw operation modes are required. When operating in such modes, the lasers experience numerous complete thermal cycles between "cold" heat sink temperature and the "hot" temperature typical of thermally equilibrated cw operation. It is clearly demonstrated that the main failure mechanism directly linked to repetitive cw operation is thermo-mechanical fatigue of the solder joints adjacent to the laser bars, especially when "soft" solders are used. Analyses of the bonding interfaces were carried out using scanning electron microscopy. It was observed that intermetallic compounds, formed already during the bonding process, lead to the solders fatigue both on the p- and n-side of the laser bar. Fatigue failure of solder joints in repetitive cw operation reduces useful lifetime of the stacks to hundreds hours, in comparison with more than 10,000 hours lifetime typically demonstrated in commonly adopted non-stop cw reliability testing programs. It is shown, that proper selection of package materials and solders, careful design of fatigue sensitive parts and burn-in screening in the hard pulse operation mode allow considerable increase of lifetime and reliability, without compromising the device efficiency, optical power density and compactness.

Fatigue Behavior of Crystalline-Reinforced Glass-Ceramics.

PubMed

Vicari, Carolina Barbosa; Magalhães, Bárbara de Oliveira; Griggs, Jason Alan; Borba, Márcia

2018-01-03

To evaluate the fatigue behavior of two crystalline-reinforced ceramics: leucite-reinforced (VL) and lithium disilicate-based (VD) glass-ceramics. Bar-shaped specimens (16 × 4 × 1.2 mm) were produced for each ceramic using prefabricated CAD/CAM blocks. For each group, 30 specimens were subjected to a three-point flexural strength test in a universal testing machine. For VL and VD, 36 and 41 specimens were subjected to a cyclic fatigue test, respectively. The cyclic fatigue test was performed with a pneumatic mechanical cycling machine (1 Hz; 37°C distilled water). Specimens were tested at two stress levels for each preset lifetime (10 3 and 10 4 cycles for VL; 10 4 and 10 5 cycles for VD) following the boundary technique. Fractography was performed with a scanning electron microscope. Data were analyzed with Weibull analysis. There were significant differences among groups for characteristic strength (σ 0 ) and Weibull modulus (m), as the confidence intervals did not overlap. The VD group presented the highest values of σ 0 , but the lowest Weibull modulus. Both groups showed a reduction of approximately 60% of the initial flexural strength (σ f ) after cycling for 10 4 cycles. For VD tested in fatigue, there was no degradation of σ f when the number of cycles was increased from 10 4 to 10 5 . The VL group showed an 18% decrease in σ f when the number of cycles increased from 10 3 to 10 4 . Flexural strength values estimated for a 5% probability of failure were 36 MPa for VL and 55 MPa for VD, after 10 4 cycles. Both glass-ceramics showed similar strength degradation (60%) after a lifetime of 10 4 cycles, despite their distinct mechanical properties. Mechanical cycling in humid conditions proved to be an important factor for the degradation of the mechanical properties of crystalline-reinforced glass-ceramics. © 2018 by the American College of Prosthodontists.

Effect of sodium hypochlorite and saline on cyclic fatigue resistance of WaveOne Gold and Reciproc reciprocating instruments.

PubMed

Elnaghy, A M; Elsaka, S E

2017-10-01

To compare the cyclic fatigue resistance of WaveOne Gold (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) and Reciproc (VDW, Munich, Germany) reciprocating instruments during immersion in sodium hypochlorite (NaOCl) and saline solutions at body temperature. A total of 180 new WaveOne Gold primary size 25, .07 taper, and Reciproc size 25, .08 taper were randomly divided into three groups: group 1: no immersion (control, air); group 2: immersion in saline at 37 ± 1 °C; and group 3: immersion in 5% NaOCl at 37 ± 1 °C. The instruments were reciprocated in the test solution until fracture, and the number of cycles to failure was recorded. The data were analysed statistically using t-tests and one-way analysis of variance (anova) with the significance level set at P < 0.05. A Weibull analysis was performed on number of cycles to failure data. WaveOne Gold instruments had significantly greater number of cycles to failure than Reciproc instruments in all groups (P < 0.001). Fatigue resistance for both instruments tested in air was significantly higher than that in saline and NaOCl solutions (P < 0.001). For both instruments, there was no significant difference in the fatigue resistance between saline and NaOCl solutions (P > 0.05). The Weibull analysis showed that the predicted cycles of WaveOne Gold in air was 1027 cycles for 99% survival. However, Reciproc instruments tested in NaOCl solution had the lowest predicted cycles (613 cycles) among the groups. Immersion of WaveOne Gold and Reciproc reciprocating instruments in saline and NaOCl solutions decreased considerably their cyclic fatigue resistance. The fatigue resistance of WaveOne Gold instruments was higher than that of Reciproc instruments. © 2016 International Endodontic Journal. Published by John Wiley & Sons Ltd.

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

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Miller, Robert A.

1998-01-01

Thick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt.% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF/HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damages at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, were observed especially for the combined LCF/HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.

Tendon fatigue in response to mechanical loading

PubMed Central

Andarawis-Puri, N.; Flatow, E. L.

2015-01-01

Tendinopathies are commonly attributable to accumulation of sub-rupture fatigue damage from repetitive use. Data is limited to late stage disease from patients undergoing surgery, motivating development of animal models, such as ones utilizing treadmill running or repetitive reaching, to investigate the progression of tendinopathies. We developed an in vivo model using the rat patellar tendon that allows control of the loading directly applied to the tendon. This manuscript discusses the response of tendons to fatigue loading and applications of our model. Briefly, the fatigue life of the tendon was used to define low, moderate and high levels of fatigue loading. Morphological assessment showed a progression from mild kinks to fiber disruption, for low to high level fatigue loading. Collagen expression, 1 and 3 days post loading, showed more modest changes for low and moderate than high level fatigue loading. Protein and mRNA expression of Ineterleukin-1β and MMP-13 were upregulated for moderate but not low level fatigue loading. Moderate level (7200 cycles) and 100 cycles of fatigue loading resulted in a catabolic and anabolic molecular profile respectively, at both 1 and 7 days post loading. Results suggest unique mechanisms for different levels of fatigue loading that are distinct from laceration. PMID:21625047

Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

NASA Technical Reports Server (NTRS)

Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

2007-01-01

An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semi-logarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

NASA Technical Reports Server (NTRS)

Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

2007-01-01

An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semilogarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

Fatigue behavior of a cross-ply ceramic matrix composite subjected to tension-tension cycling with hold time. Master`s thesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grant, S.A.

This study was carried out to investigate the elevated temperature behavior of the SiC-MAS5 cross- ply (O/9O)4S ceramic matrix composite manufactured by Corning Inc. to fatigue with loading waveforms that combine the characteristics of stress rupture and high cycle fatigue. The test results were compiled in the form of S-N (cycles to failure), S-T (exposure time versus cycles to failure), S-S (energy exposure versus cycles to failure), normalized modulus degradation, strain progression, and hysteresis loop progression. From the mechanical behavior demonstrated by these curves, relationships between the effect of the environment and loading waveform were developed. In addition, a post-mortemmore » SEM analysis of the fracture surface was conducted and the results compared to the mechanical behavior.« less

Effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate thin films: Experimental evidence and implications

NASA Astrophysics Data System (ADS)

Lou, X. J.; Zhang, H. J.; Luo, Z. D.; Zhang, F. P.; Liu, Y.; Liu, Q. D.; Fang, A. P.; Dkhil, B.; Zhang, M.; Ren, X. B.; He, H. L.

2014-09-01

The effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate (PZT) thin film was systematically investigated. It was found that electrical fatigue strongly affects the Rayleigh behaviour of the PZT film. Both the reversible and irreversible Rayleigh coefficients decrease with increasing the number of switching cycles. This phenomenon is attributed to the growth of an interfacial degraded layer between the electrode and the film during electrical cycling. The methodology used in this work could serve as an alternative way for evaluating the fatigue endurance and degradation in dielectric properties of ferroelectric thin-film devices during applications.

Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jianfeng; Xuan, Fu-Zhen, E-mail: fzxuan@ecust.edu.cn

The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

Markov model of fatigue of a composite material with the poisson process of defect initiation

NASA Astrophysics Data System (ADS)

Paramonov, Yu.; Chatys, R.; Andersons, J.; Kleinhofs, M.

2012-05-01

As a development of the model where only one weak microvolume (WMV) and only a pulsating cyclic loading are considered, in the current version of the model, we take into account the presence of several weak sites where fatigue damage can accumulate and a loading with an arbitrary (but positive) stress ratio. The Poisson process of initiation of WMVs is considered, whose rate depends on the size of a specimen. The cumulative distribution function (cdf) of the fatigue life of every individual WMV is calculated using the Markov model of fatigue. For the case where this function is approximated by a lognormal distribution, a formula for calculating the cdf of fatigue life of the specimen (modeled as a chain of WMVs) is obtained. Only a pulsating cyclic loading was considered in the previous version of the model. Now, using the modified energy method, a loading cycle with an arbitrary stress ratio is "transformed" into an equivalent cycle with some other stress ratio. In such a way, the entire probabilistic fatigue diagram for any stress ratio with a positive cycle stress can be obtained. Numerical examples are presented.

Effect of stress ratio on the fatigue behaviour of glass/epoxy composite

NASA Astrophysics Data System (ADS)

Syayuthi, A. R. A.; Majid, M. S. Abdul; Ridzuan, M. J. M.; Basaruddin, K. S.; Peng, T. L.

2017-10-01

The effect of stress ratio on the fatigue behaviour of the GFRE composite has been investigated. The glass fibre reinforced epoxy (GFRE) composite plates were fabricated using vacuum infusion method. Static tensile was performed in accordance with the ASTM D5766 standard, and the cyclic test was conducted according to ASTM D3479 with three different stress ratio, R = 0, 0.5, -1. Static tensile tests were carried out to determine the ultimate strength of this composite. Subsequently, fatigue tests loads ranging from 30% to 90% of the ultimate load were applied to each specimen. The S-N curve of different stress ratio loading of fibreglass/epoxy composites was then established. The results show that the number of cycles to failure increases as the loading is decreased. The specimens for fatigue tests loads 30% at R = 0 and -1 recorded the highest number of cycles at 2 million cycles. The results obtained from this test indicated a significant life reduction for R = -1 compared with the tension-tension loading, with the life reduction for R = -1 being greatest. The fatigue behaviour of the GFRE composite materials is not only influenced by the percentage of fatigue tests load but with different of stress ratio.

Thermal-stress fatigue behavior of twenty-six superalloys

NASA Technical Reports Server (NTRS)

Bizon, P. T.; Spera, D. A.

1976-01-01

The comparative thermal-stress fatigue resistances of 26 nickeland cobalt-base alloys were determined by fluidized bed tests. Cycles to cracking differed by almost three orders of magnitude for these materials, with directional solidification and surface protection showing definite benefit. The alloy-coating combination with the highest thermal-stress fatigue resistance was directionally solidified NASA TAZ-8A with an RT-SP coating. Its oxidation resistance was also excellent, showing approximately a 1/2 percent weight loss after 14,000 fluidized bed cycles.

On massive carbide precipitation during high temperature low cycle fatigue in alloy 800H

NASA Technical Reports Server (NTRS)

Sankararao, K. Bhanu; Schuster, H.; Halford, G. R.

1994-01-01

The effect of strain rate on massive precipitation and the mechanism for the occurrence of massive precipitation of M23C6 in alloy 800H is investigated during elevated temperature low cycle fatigue testing. It was observed that large M23C6 platelets were in the vicinity of grain and incoherent twin boundaries. The strain controlled fatigue testing at higher strain rates that promoted cyclic hardening enabled massive precipitation to occur more easily.

Load fatigue performance of four implant-abutment interface designs: effect of torque level and implant system.

PubMed

Quek, H C; Tan, Keson B; Nicholls, Jack I

2008-01-01

Biomechanical load-fatigue performance data on single-tooth implant systems with different implant-abutment interface designs is lacking in the literature. This study evaluated the load fatigue performance of 4 implant-abutment interface designs (Brånemark-CeraOne; 3i Osseotite-STA abutment; Replace Select-Easy abutment; and Lifecore Stage-1-COC abutment system). The number of load cycles to fatigue failure of 4 implant-abutment designs was tested with a custom rotational load fatigue machine. The effect of increasing and decreasing the tightening torque by 20% respectively on the load fatigue performance was also investigated. Three different tightening torque levels (recommended torque, -20% recommended torque, +20% recommended torque) were applied to the 4 implant systems. There were 12 test groups with 5 samples in each group. The rotational load fatigue machine subjected specimens to a sinusoidally applied 35 Ncm bending moment at a test frequency of 14 Hz. The number of cycles to failure was recorded. A cutoff of 5 x 10(6) cycles was applied as an upper limit. There were 2 implant failures and 1 abutment screw failure in the Brånemark group. Five abutment screw failures and 4 implant failures was recorded for the 3i system. The Replace Select system had 1 implant failure. Five cone screw failures were noted for the Lifecore system. Analysis of variance revealed no statistically significant difference in load cycles to failure for the 4 different implant-abutment systems torqued at recommended torque level. A statistically significant difference was found between the -20% torque group and the +20% torque group (P < .05) for the 3i system. Load fatigue performance and failure location is system specific and related to the design characteristics of the implant-abutment combination. It appeared that if the implant-abutment interface was maintained, load fatigue failure would occur at the weakest point of the implant. It is important to use the torque level recommended by the manufacturer.

Interconnect fatigue design for terrestrial photovoltaic modules

NASA Technical Reports Server (NTRS)

Mon, G. R.; Moore, D. M.; Ross, R. G., Jr.

1982-01-01

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field.

Interconnect fatigue design for terrestrial photovoltaic modules

NASA Astrophysics Data System (ADS)

Mon, G. R.; Moore, D. M.; Ross, R. G., Jr.

1982-03-01

The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Exploratory Thermal-mechanical Fatigue Results for Rene' 80 in Ultrahigh Vacuum

NASA Technical Reports Server (NTRS)

Sheinker, A. A.

1978-01-01

A limited study was conducted of the use of strainage partitioning for predicting the thermalmechanical fatigue life of cast nickel-base superalloy Rene' 80. The fatigue lives obtained by combined inphase thermal and mechanical strain cycling between 400 C (752 F) and 1000 C (1802 F) in an ultrahigh vacuum were considerably shorter than those represented by the four basic partitioned inelastic strainrange fatigue life relationships established previously for this alloy at 871 C (1600 F) and 1000 C (1832 F) in an ultrahigh vacuum. This behavior was attributed to the drastic decrease in ductility with decreasing temperature for this alloy. These results indicated that the prediction of the thermal-mechanical fatigue life of Rene' 80 by the method of strainrange partioning may be improved if based on the four basic fatigue life relationships determined at a lower temperature in the thermal-mechanical strain cycle.

The direct-stress fatigue strength of 17S-T aluminum alloy throughout the range from 1/2 to 500,000,000 cycles of stress

NASA Technical Reports Server (NTRS)

Hartmann, E C; Stickley, G W

1942-01-01

Fatigue-test were conducted on six specimens made from 3/4-inch-diameter 17S-T rolled-and-drawn rod for the purpose of obtaining additional data on the fatigue life of the material at stresses up to the static strength. The specimens were tested in direct tension using a stress range from zero to a maximum in tension. A static testing machine was used to apply repeated loads in the case of the first three specimens; the other three specimens were tested in a direct tension-compression fatigue machine. The direct-stress fatigue curve obtained for the material indicates that, in the range of stresses above about two-thirds the tensile strength, the fatigue strength is higher than might be expected by simply extrapolating the ordinary curve of stress plotted against the number of cycles determined at lower stresses.

Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions

NASA Astrophysics Data System (ADS)

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

2014-10-01

Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.

Low-Cycle Fatigue Properties of P92 Ferritic-Martensitic Steel at Elevated Temperature

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Hu, ZhengFei; Schmauder, Siegfried; Mlikota, Marijo; Fan, KangLe

2016-04-01

The low-cycle fatigue behavior of P92 ferritic-martensitic steel and the corresponding microstructure evolution at 873 K has been extensively studied. The test results of fatigue lifetime are consistent with the Coffin-Manson relationship over a range of controlled total strain amplitudes from 0.15 to 0.6%. The influence of strain amplitude on the fatigue crack initiation and growth has been observed using optical microscopy and scanning electron microscopy. The formation mechanism of secondary cracks is established according to the observation of fracture after fatigue process and there is an intrinsic relationship between striation spacing, current crack length, and strain amplitude. Transmission electron microscopy has been employed to investigate the microstructure evolution after fatigue process. It indicates the interaction between carbides and dislocations together with the formation of cell structure inhibits the cyclic softening. The low-angle sub-boundary elimination in the martensite is mainly caused by the cyclic stress.

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

NASA Astrophysics Data System (ADS)

Sun, Chengqi; Liu, Xiaolong; Hong, Youshi

2015-06-01

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

Some aspects of thermomechanical fatigue of AISI 304L stainless steel: Part I. creep- fatigue damage

NASA Astrophysics Data System (ADS)

Zauter, R.; Christ, H. J.; Mughrabi, H.

1994-02-01

Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under “true≓ plastic-strain control in vacuum. This report considers the damage oc-curring during TMF loading. It is shown how the temperature interval and the phasing (in-phase, out-of-phase) determine the mechanical response and the lifetime of the specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the ma-terial, leading to intergranular cracks which reduce the lifetime considerably. Out-of-phase cy-cling inhibits creep-induced damage, and no lifetime reduction occurs, even if the material is exposed periodically to temperatures in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a given strain rate, the formula is able to estimate the temperature of transition between pure fatigue and creep-fatigue damage.

Procedures for characterizing an alloy and predicting cyclic life with the total strain version of Strainrange Partitioning

NASA Technical Reports Server (NTRS)

Saltsman, James F.; Halford, Gary R.

1989-01-01

Procedures are presented for characterizing an alloy and predicting cyclic life for isothermal and thermomechanical fatigue conditions by using the total strain version of strainrange partitioning (TS-SRP). Numerical examples are given. Two independent alloy characteristics are deemed important: failure behavior, as reflected by the inelastic strainrange versus cyclic life relations; and flow behavior, as indicated by the cyclic stress-strain-time response (i.e., the constitutive behavior). Failure behavior is characterized by conducting creep-fatigue tests in the strain regime, wherein the testing times are reasonably short and the inelastic strains are large enough to be determined accurately. At large strainranges, stress-hold, strain-limited tests are preferred because a high rate of creep damage per cycle is inherent in this type of test. At small strainranges, strain-hold cycles are more appropriate. Flow behavior is characterized by conducting tests wherein the specimen is usually cycled far short of failure and the wave shape is appropriate for the duty cycle of interest. In characterizing an alloy pure fatigue, or PP, failure tests are conducted first. Then depending on the needs of the analyst a series of creep-fatigue tests are conducted. As many of the three generic SRP cycles are featured as are required to characterize the influence of creep on fatigue life (i.e., CP, PC, and CC cycles, respectively, for tensile creep only, compressive creep only, and both tensile and compressive creep). Any mean stress effects on life also must be determined and accounted for when determining the SRP inelastic strainrange versus life relations for cycles featuring creep. This is particularly true for small strainranges. The life relations thus are established for a theoretical zero mean stress condition.

Influence of Endodontic Treatment and Retreatment on the Fatigue Failure Load, Numbers of Cycles for Failure, and Survival Rates of Human Canine Teeth.

PubMed

Missau, Taiane; De Carlo Bello, Mariana; Michelon, Carina; Mastella Lang, Pauline; Kalil Pereira, Gabriel; Baldissara, Paolo; Valandro, Luiz Felipe; Souza Bier, Carlos Alexandre; Pivetta Rippe, Marília

2017-12-01

This study evaluated the effects of endodontic treatment and retreatment on the fatigue failure load, numbers of cycles for failure, and survival rates of canine teeth. Sixty extracted canine teeth, each with a single root canal, were selected and randomly divided into 4 groups (n = 15): untreated, teeth without endodontic intervention; prepared, teeth subjected only to rotary instrumentation; filled, teeth receiving complete endodontic treatment; and retreated, teeth retreated endodontically. After the different endodontic interventions, the specimens were subjected to fatigue testing by the stepwise method: 200 N (× 5000 load pulses), 300 N, 400 N, 500 N, 600 N, 800 N, and 900 N at a maximum of 30,000 load pulses each or the occurrence of fracture. Data from load to failure and numbers of cycles for fracture were recorded and subjected to Kaplan-Meier and Log Rank tests (P < .05), in addition to Weibull analysis. The fractures of the specimens were classified as repairable or catastrophic. The retreated, filled, and untreated groups presented statistically significantly higher fatigue failure loads and numbers of cycles for failure than did the prepared group. Weibull analysis showed no statistically significant difference among the treatments for characteristic load to failure and characteristic number of cycles for failure, although, for number of cycles, a higher Weibull modulus was observed in filled and retreated conditions. The predominant mode of failure was catastrophic. Teeth subjected to complete endodontic treatment and retreatment behaved similarly in terms of fatigue failure load and number of cycles to failure when compared with untreated teeth. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Life prediction of expulsion bladders through fatigue test and fold strain analysis

NASA Technical Reports Server (NTRS)

Chu, H. N.; Unterberg, W.

1972-01-01

Cycle life data are presented in terms of true maximum strain for four metals, two plastics, and two elastomers. The Coffin-Manson fatigue theory was applied for metals and plastics, and cut-growth fatigue theory for elastomers. The data are based on measurements made at room and elevated temperatures. It was found that double folds give rise to far severer folding strains than do simple folds. It was also found that, except for the elastomers, all the bladder materials develop surface cracks due to double folds after only one cycle. The findings indicate that metals, which are bets for premeation resistance, are worst for fatigue resistance, and vice versa for elastomers. The intermediate plastics were found to be unsatisfactory for both permeation and fatigue resistance for missions of extended duration.

High Cycle Fatigue Properties Of Electron Beam Melted TI-6AL-4V Samples Without And With Integrated Defects ("Effects Of Defects")

NASA Astrophysics Data System (ADS)

Brandl, Erhard; Greitemeier, Daniel; Maier, Hans Jurgen; Syassen, Freerk

2012-07-01

The understanding of additive manufactured material properties is still at an early stage and mostly not profound. Nowadays, there is only little experience in predicting the effect of defects (e.g. porosity, unmelted spots, insufficient bonding between the layers) on the fatigue behaviour. In this paper, some of these questions are adressed. An electron beam melting process is used to manufacture Ti-6Al-4V high cycle fatigue samples without and with intentionally integrated defects inside of the samples. The samples were annealed or hot isostatically pressed. The defects were analysed by non- destructive methods before and by light/electron microscopy after the tests. In order to predict the high cycle fatigue properties, the crack propagation properties of the material (da/dN - ΔK curve) were tested and AFGROW simulation was used.

Effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue regime

NASA Astrophysics Data System (ADS)

Gu, Chao; Bao, Yan-ping; Gan, Peng; Wang, Min; He, Jin-shan

2018-06-01

This work aims to investigate the effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue (VHCF) regime. The size and type of inclusions in the steel were quantitatively analyzed, and VHCF tests were performed. Some fatigue cracks were found to be initiated in the gaps between inclusions (Al2O3, MgO-Al2O3) and the matrix, while other cracks originated from the interior of inclusions (TiN, MnS). To explain the related mechanism, the tessellated stresses between inclusions and the matrix were calculated and compared with the yield stress of the matrix. Results revealed that the inclusions could be classified into two types under VHCF; of these two, only one type could be regarded as holes. Findings in this research provide a better understanding of how inclusions affect the high cycle fatigue properties of bearing steel.

Assessment of Musculoskeletal Strength and Levels of Fatigue during Different Phases of Menstrual Cycle in Young Adults

PubMed Central

D Souza, Urban John; Shivaprakash, G

2017-01-01

Introduction Some of the physiological factors and athletic performance might show variation along the phases of menstrual cycle. The alterations seen in these physiological parameters of various systems relating to oscillations in hormonal levels do affect the autonomic nervous system and metabolic functions. Former studies heave inconclusively about the influence of hormones on exercise performance, predominantly muscle strength and rate of fatigue during different phases of the menstrual cycle. Studies regarding influence of these variations during bleeding phase were not done. Aim To evaluate the muscle strength variations and also the rate of fatigue during various phases of the menstrual cycle in young adults. Materials and Methods This was a prospective study conducted among 100 healthy adult female volunteers aged 18-24 years, with normal regular menstrual cycles persistent between 26- 32 days (average of 28 days), for a minimum of last 6 months. Muscle strength was assessed by calculating the work done and fatigue rate using Mosso’s ergograph and by handgrip dynamometer strength. Each subject was evaluated consecutively for two menstrual cycles in all three phases which were classified as Phase 1- Menstrual phase, Phase 2- Follicular phase and Phase 3- Luteal phase. The data obtained was analysed by statistical tool One-way ANOVA followed by a post-hoc Tukeys test. A p-value of ≤ 0.05 was considered significant. Results The amount of work done and handgrip strength was significantly higher in phase 2 (p<0.001) and relatively reduced in phase 1 and 3 (p<0.001) of menstrual cycle. In terms of fatigue rate percentage, phase 2 showed significantly lesser values (p<0.001) as compared to phase 1 and 3 of menstrual cycle. Conclusion We conclude that the cyclical variation in endogenous reproductive hormones increases the muscle strength in follicular phase of the menstrual cycle. Thus provide support for the influence of these hormones in regulation of these parameters in the premenopausal age group. PMID:28384857

Estimation of Axial Fretting Fatigue Life at Elevated Temperatures Using Critical Distance Theory

NASA Astrophysics Data System (ADS)

Majzoobi, G. H.; Azhdarzadeh, P.

Fretting fatigue life is traditionally estimated by experiment. The objective of this work is to introduce a special approach for estimation of axial fretting fatigue life at elevated temperatures from plain fatigue test based on the critical distance theory. The method uses Fatemi-Socie parameter as a multiaxial criterion to compute the stress multiaxiality on focus path. This method considers only elastic behavior for materials, and two characteristic diagrams are obtained from plain fatigue tests on two U-shaped and V-shaped notched specimens. The results showed reasonable agreement between the predictions by the proposed method and the experiments for ambient temperature. For elevated temperatures, the results indicated that the predicted fretting fatigue life was considerably overestimated in the low cycle fatigue (LCF) regime and underestimated in the high cycle fatigue (HCF) region with respect to experimental measurements. The reason for such discrepancy is believed to be due to the complex behavior of AL 7075-T6, which exhibits at elevated temperatures because of the problems such as aging, oxidation and reduction of strength.

Crack initiation and propagation in 50.9 at. pct Ni-Ti pseudoelastic shape-memory wires in bending-rotation fatigue

NASA Astrophysics Data System (ADS)

Sawaguchi, Tak Ahiro; Kausträter, Gregor; Yawny, Alejandro; Wagner, Martin; Eggeler, Gunther

2003-12-01

The structural fatigue of pseudoelastic Ni-Ti wires (50.9 at. pct Ni) was investigated using bending-rotation fatigue (BRF) tests, where a bent and otherwise unconstrained wire was forced to rotate at different rotational speeds. The number of cycles to failure ( N f ) was measured for different bending radii and wire thicknesses (1.0, 1.2, and 1.4 mm). The wires consisted of an alloy with a 50-nm grain size, no precipitates, and some TiC inclusions. In BRF tests, the surface of the wire is subjected to tension-compression cycles, and fatigue lives can be related to the maximum tension and compression strain amplitudes ( ɛ a ) in the wire surface. The resulting ɛ a - N f curves can be subdivided into three regimes. At ɛ a > 1 pct rupture occurs early (low N f ) and the fatigue-rupture characteristics were strongly dependent on ɛ a and the rotational speed (regime 1). For 0.75 pct < ɛ a < 1 pct, fatigue lives strongly increase and are characterized by a significant statistical scatter (regime 2). For ɛ a < 0.75 pct, no fatigue rupture occurs up to cycle numbers of 106 (regime 3). Using scanning electron microscopy (SEM), it was shown that surface cracks formed in regions with local stress raisers (such as inclusions and/or scratches). The growth of surface cracks during fatigue loading produced striations on the rupture surface; during final rupture, ductile voids form. The microstructural details of fatigue-damage accumulation during BRF testing are described and discussed.

Estimation of Low Cycle Fatigue Response of 316 LN Stainless Steel in the Presence of Notch

NASA Astrophysics Data System (ADS)

Agrawal, Richa; Veerababu, J.; Goyal, Sunil; Sandhya, R.; Uddanwadiker, Rashmi; Padole, Pramod

2018-02-01

Notches introduced in the plain specimen result in the multiaxial state of stress that exists in the actual components due to the presence of flaws and defects. In the present work, low cycle fatigue life estimation of plain and notched specimens of 316 LN stainless steel is carried out at room temperature and 823 K. The plain and notched specimens with different notch radii were subjected to varying strain amplitudes ranging from ± 0.25 to ± 1.0% at a strain rate of 3 × 10-3 s-1. The fatigue life decreased in the presence of notch for all strain amplitudes at both the temperatures. The decrease in fatigue life was found to be more at room temperature than at 823 K. The fatigue life of the notched specimen decreased by approximately 94.2% compared to plain specimen at room temperature. However, at 823 K the decrease in fatigue life for notched specimen was approximately 84.6%. Low cycle fatigue life of the plain and notched specimens was estimated by Neuber's rule and finite element analysis approach. Neuber's rule overestimated the fatigue life by maximum factor of 2.6 for specimens at room temperature and by maximum factor of 5 for specimens at 823 K. However, it gives closer approximation at higher strain amplitudes at 823 K. Life estimation by finite element analysis at room temperature was within a factor of 1.5 as compared to experimental life, whereas it underestimated the fatigue life within a factor of 6 at high temperature.

Locomotor Muscle Fatigue Does Not Alter Oxygen Uptake Kinetics during High-Intensity Exercise.

PubMed

Hopker, James G; Caporaso, Giuseppe; Azzalin, Andrea; Carpenter, Roger; Marcora, Samuele M

2016-01-01

The [Formula: see text] slow component ([Formula: see text]) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min -1 . Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and [Formula: see text] determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue ( P = 0.03), the [Formula: see text] was not significantly different between the pre-fatigue (464 ± 301 mL·min -1 ) and the control (556 ± 223 mL·min -1 ) condition ( P = 0.50). Blood lactate response was not significantly different between conditions ( P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition ( P < 0.01) suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the [Formula: see text] kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the [Formula: see text] is strongly associated with locomotor muscle fatigue.

Effect of Understress on Fretting Fatigue Crack Initiation of Press-Fitted Axle

NASA Astrophysics Data System (ADS)

Kubota, Masanobu; Niho, Sotaro; Sakae, Chu; Kondo, Yoshiyuki

Axles are one of the most important components in railway vehicles with regard to safety, since a fail-safe design is not available. The problems of fretting fatigue crack initiation in a press-fitted axle have not been completely solved even though up-to-date fatigue design methods are employed. The objective of the present study is to clarify the effect of understress on fretting fatigue crack initiation behavior in the press-fitted axle. Most of the stress amplitude given to the axle in service is smaller than the fretting fatigue limit based on the stress to initiate cracks under a constant load σwf1. Rotating bending fatigue tests were performed using a 40mm-diameter press-fitted axle assembly. Two-step variable stresses consisting of σwf1 and half or one-third of σwf1 were used in the experiment. Crack initiation life was defined as the number of cycles when a fretting fatigue crack, which is longer than 30µm, was found using a metallurgical microscope. Fretting fatigue cracks were initiated even when the variable stress did not contain the stress above the fretting fatigue crack initiation limit. The crack initiation life varied from 4.0×107 to 1.2×108 depending on the stress frequency ratio nL/nH. The sum of the number of cycles of higher stress at crack initiation NH was much smaller than the number of cycles to initiate cracks estimated from the modified Miner's rule. The value of the modified Miner's damage ranged from 0.013 to 0.185. To clarify the effect of variable amplitude on the fretting fatigue crack initiation, a comprehensive investigation related to relative slip, tangential force and fretting wear is necessary.

Locomotor Muscle Fatigue Does Not Alter Oxygen Uptake Kinetics during High-Intensity Exercise

PubMed Central

Hopker, James G.; Caporaso, Giuseppe; Azzalin, Andrea; Carpenter, Roger; Marcora, Samuele M.

2016-01-01

The V˙O2 slow component (V˙O2sc) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min−1. Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and V˙O2max determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue (P = 0.03), the V˙O2sc was not significantly different between the pre-fatigue (464 ± 301 mL·min−1) and the control (556 ± 223 mL·min−1) condition (P = 0.50). Blood lactate response was not significantly different between conditions (P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition (P < 0.01) suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the V˙O2 kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the V˙O2sc is strongly associated with locomotor muscle fatigue. PMID:27790156

Identification of distinct fatigue trajectories in patients with breast cancer undergoing adjuvant chemotherapy.

PubMed

Junghaenel, Doerte U; Cohen, Jules; Schneider, Stefan; Neerukonda, Anu R; Broderick, Joan E

2015-09-01

The goal of this study was to characterize changes in daily fatigue in women undergoing chemotherapy for breast cancer. We examined whether there are subgroups of patients with distinct fatigue trajectories and explored potential psychosocial and biomedical predictors of these subgroups. Participants were 77 women with breast cancer receiving adjuvant chemotherapy with AC-T (2-week cycle) and TC or TCH (3-week cycle) regimens. They completed 28 daily ratings online using an adapted version of the Patient-Reported Outcomes Measurement Information System (PROMIS®) fatigue instrument. Both regimens followed an "inverted-U-shaped" fatigue pattern over approximately 2 weeks. Growth mixture modeling identified three patient subgroups with distinct trajectories. Fatigue scores in the "low fatigue" group (23 %) increased following the infusion and quickly abated. The "transient fatigue" (27 %) group had a very pronounced increase. Patients in the "high fatigue" (50 %) group reported consistently elevated fatigue with a relatively small increase. Demographic and medical variables were not associated with fatigue trajectory. Patients in the "high fatigue" group reported significantly poorer physical, emotional, and social functioning, poorer general health, and more depressed mood than patients in the "low fatigue" group. The "transient fatigue" group reported significantly better physical and social functioning than the "high fatigue" group, but emotional distress and depression similar to the "high fatigue" group. The identification of patient subgroups with distinct fatigue trajectories during chemotherapy is an essential step for developing preventative strategies and tailored interventions. Our results suggest that different trajectories are associated with patients' psychosocial and general health.

A Pilot Exploration of Symptom Trajectories in Adolescents with Cancer during Chemotherapy

PubMed Central

Ameringer, Suzanne; Elswick, R. K.; Shockey, Debra P.; Dillon, Robyn

2012-01-01

Background Chemotherapy is frequently administered in repetitive cycles. Adolescents with cancer suffer from multiple symptoms related to chemotherapy but knowledge of symptom trajectories across a cycle is limited. Examining trajectories over a cycle may reveal key periods to manage symptoms. Objectives The aims of this pilot were to describe the trajectory of symptoms (pain, sleep, fatigue, appetite, nausea, fatigue) and biological and behavioral variables (anxiety, stress, hematologic function) across one cycle; and examine relationships between variables. Interventions/Methods Nine adolescents with cancer within six months of diagnosis participated. Data were collected by surveys, chart review, and biologic measures on days 1 and 2 of the cycle, one week later (nadir), and day 1 of the following cycle. To evaluate the trajectory, a simple random effects repeated measures analysis was computed. Results The significant trajectories were fatigue (P = 0.003), difficulty sleeping (P = 0.032), and nausea (P = 0.04). Most of the adolescents reported some anticipatory anxiety about receiving chemotherapy. Significant correlations between symptoms and biobehavioral variables included anticipatory anxiety and nausea (P = 0.86, P = 0.003), trait anxiety and fatigue (r = −0.82, P < 0.001), and stress and pain (r = 0.78, P = 0.039). Conclusions Multiple symptoms were experienced across the cycle. Three symptoms displayed significant trajectories indicating that patterns of symptoms may be anticipated. Implications for Practice Pilot findings suggest monitoring symptoms, stress and anxiety across a cycle is important, not only during chemotherapy administration, but also prior to being admitted for chemotherapy. PMID:22561919

Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes.

PubMed

Lepers, R; Theurel, J; Hausswirth, C; Bernard, T

2008-07-01

The aim of this study was to determine whether or not variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age: 33+/-5 years, mass: 74+/-4 kg, VO2max: 62+/-5 mL kg(-1) min(-1), maximal aerobic power: 392+/-17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating +/-15%, +/-5%, and +/-10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal voluntary activation level and excitation-contraction coupling process of knee extensor muscles were evaluated before and immediately after the exercise using the technique of electrically evoked contractions (single and paired stimulations). Oxygen uptake, ventilation and heart rate were also measured at regular intervals during the exercise. Averaged metabolic variables were not significantly different between the two conditions. Similarly, reductions in MVC torque (approximately -11%, P<0.05) after cycling were not different (P>0.05) between CP and VP trials. The magnitude of central and peripheral fatigue was also similar at the end of the two cycling exercises. It is concluded that, following 30 min of endurance cycling, semi-elite triathletes experienced no additional neuromuscular fatigue by varying power (from +/-5% to 15%) compared with a protocol that involved a constant power.

The effects of multiple repairs on Inconel 718 weld mechanical properties

NASA Technical Reports Server (NTRS)

Russell, C. K.; Nunes, A. C., Jr.; Moore, D.

1991-01-01

Inconel 718 weldments were repaired 3, 6, 9, and 13 times using the gas tungsten arc welding process. The welded panels were machined into mechanical test specimens, postweld heat treated, and nondestructively tested. Tensile properties and high cycle fatigue life were evaluated and the results compared to unrepaired weld properties. Mechanical property data were analyzed using the statistical methods of difference in means for tensile properties and difference in log means and Weibull analysis for high cycle fatigue properties. Statistical analysis performed on the data did not show a significant decrease in tensile or high cycle fatigue properties due to the repeated repairs. Some degradation was observed in all properties, however, it was minimal.

Multiple Fatigue Failure Behaviors and Long-Life Prediction Approach of Carburized Cr-Ni Steel with Variable Stress Ratio

PubMed Central

Deng, Hailong; Li, Wei; Zhao, Hongqiao; Sakai, Tatsuo

2017-01-01

Axial loading tests with stress ratios R of −1, 0 and 0.3 were performed to examine the fatigue failure behavior of a carburized Cr-Ni steel in the long-life regime from 104 to 108 cycles. Results show that this steel represents continuously descending S-N characteristics with interior inclusion-induced failure under R = −1, whereas it shows duplex S-N characteristics with surface defect-induced failure and interior inclusion-induced failure under R = 0 and 0.3. The increasing tension eliminates the effect of compressive residual stress and promotes crack initiation from the surface or interior defects in the carburized layer. The FGA (fine granular area) formation greatly depends on the number of loading cycles, but can be inhibited by decreasing the compressive stress. Based on the evaluation of the stress intensity factor at the crack tip, the surface and interior failures in the short life regime can be characterized by the crack growth process, while the interior failure with the FGA in the long life regime can be characterized by the crack initiation process. In view of the good agreement between predicted and experimental results, the proposed approach can be well utilized to predict fatigue lives associated with interior inclusion-FGA-fisheye induced failure, interior inclusion-fisheye induced failure, and surface defect induced failure. PMID:28906454

Electronic diary evidence on energy erosion in clinical burnout.

PubMed

Sonnenschein, Mieke; Sorbi, Marjolijn J; van Doornen, Lorenz J P; Schaufeli, Wilmar B; Maas, Cora J M

2007-10-01

Burnout is generally defined as a state of severe exhaustion. So far, research has predominantly focused on relatively mild burnout in employees able to work despite their complaints. This study examines energy depletion in clinical burnout (e.g., the severest cases on extended sick leave) by comparing the diurnal patterns of fatigue and exhaustion with those of healthy individuals. Sixty clinically burned-out and 40 healthy participants kept an electronic diary for 14 days, 7 times a day, yielding a total of 8,116 diary entries. This study shows that burned-out individuals typically suffer continuously from a severe fatigue throughout the day. The resulting flattened diurnal cycles mark a stable exhaustion that is uncommon in healthy persons. The current results provide novel support for the existence of severe energy erosion in clinical burnout.

Damage mechanisms in alloy 800H under creep-fatigue conditions

NASA Astrophysics Data System (ADS)

Mu, Z.; Bothe, K.; Gerold, V.

1994-05-01

The interaction between fatigue damage (i.e., fatigue crack propagation) and internal grain boundary damage (i.e., cavity formation at grain boundaries) has been studied for the Alloy 800H at 750 C for constant plastic strain ranges but different experimental conditions. Most experiments were performed at constant ranges of alternating tensile/compression stresses. Symmetrical as well as asymmetrical tests (with larger compression stresses) were performed. In comparison to the former tests, asymmetrical tests led to shorter cyclic lifetimes mainly due to cavity formation which was not observed for symmetrical tests. It could be shown that a fast compressive and a slow tensile half cycle (at large compressive and low tensile stresses) are ideal conditions for the nucleation and growth of cavities. Based on quantitative measurements of the cavity density from interrupted fatigue tests, a physical model is presented which can predict the number of cycles to failure. This cycle number is determined only by fatigue crack growth which is controlled by (1) athermal plastic deformation, (2) creep deformation and (3) rate enhancement by cavitation.

Fatigue strength degradation of metals in corrosive environments

NASA Astrophysics Data System (ADS)

Adasooriya, N. D.; Hemmingsen, T.; Pavlou, D.

2017-12-01

Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.

Solute transport during the cyclic oxidation of Ni-Cr-Al alloys. M.S. Thesis

NASA Technical Reports Server (NTRS)

Nesbitt, J. A.

1982-01-01

Important requirements for protective coatings of Ni-Cr-Al alloys for gas turbine superalloys are resistance to oxidation accompanied by thermal cycling, resistance to thermal fatigue cracking. The resistance to oxidation accompanied by thermal cycling is discussed. The resistance to thermal fatigue cracking is also considered.

78 FR 44052 - Airworthiness Directives; Sikorsky Aircraft Corporation (Sikorsky) Model Helicopters

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-23

... a regulatory distinction; and 4. Will not have a significant economic impact, positive or negative... events (LCF1) and partial low cycle fatigue events (LCF2) as those terms are defined in the... the full and partial low fatigue cycle events and record on the component card or equivalent record...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holcomb, Gordon R.

A presentation of the US-UK Phase 3 Task 1 Oxidation in Supercritical Fluids. Includes slides on Supercritical Steam, sCO 2 Power Cycles – Indirect, sCO 2 Power Cycles – Direct, Experimental Exposures, Alloys, Why Si, Results—Ni-xCr Alloys (5-24Cr), Fatigue Crack Growth$-$Experiment, and Alloys and Samples, Fatigue Crack Growth—Results (H282).

Fatigue in the Presence of Corrosion (Fatigue sous corrosion)

DTIC Science & Technology

1999-03-01

Fatigue Crack Growth Propagation of Aluminum Lithium cycle managers to safely delay repairs to a more appropriate Alloys " described the effect of... effects of service corrosion on fatigue lab tests with 2024 -T3, because 7178 life , if any, can be established in this was not available. However, we did not... life and the fatigue crack growth behavior of the cases where a structural member is the 2024 alloy was studied as well. stressed or fatigued

Transient thermal stresses analysis and thermal fatigue damage evaluation for skirt attachment of coke drum

NASA Astrophysics Data System (ADS)

Ambarita, H.; Siahaan, A. S.; Kawai, H.; Daimaruya, M.

2018-02-01

In the last decade, the demand for delayed coking capacity has been steadily increasing. The trend in the past 15 to 20 years has been for operators to try to maximize the output of their units by reducing cycle times. This mode of operation can result in very large temperature gradients within the drums during preheating stage and even more so during the quench cycle. This research provide the optimization estimation of fatigue life due to each for the absence of preheating stage and cutting stage. In the absence of preheating stage the decreasing of fatigue life is around 19% and the increasing of maximum stress in point 5 of shell-to-skirt junction is around 97 MPa. However for the absence of cutting stage it was found that is more severe compare to normal cycle. In this adjustment fatigue life reduce around 39% and maximum stress is increased around 154 MPa. It can concluded that for cycle optimization, eliminating preheating stage possibly can become an option due to the increasing demand of delayed coking process.

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants

PubMed Central

Yu, Zheng-Yong; Liu, Qiang; Liu, Yunhan

2017-01-01

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi–Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings. PMID:28792487

Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants.

PubMed

Yu, Zheng-Yong; Zhu, Shun-Peng; Liu, Qiang; Liu, Yunhan

2017-08-09

Based on the critical plane approach, a simple and efficient multiaxial fatigue damage parameter with no additional material constants is proposed for life prediction under uniaxial/multiaxial proportional and/or non-proportional loadings for titanium alloy TC4 and nickel-based superalloy GH4169. Moreover, two modified Ince-Glinka fatigue damage parameters are put forward and evaluated under different load paths. Results show that the generalized strain amplitude model provides less accurate life predictions in the high cycle life regime and is better for life prediction in the low cycle life regime; however, the generalized strain energy model is relatively better for high cycle life prediction and is conservative for low cycle life prediction under multiaxial loadings. In addition, the Fatemi-Socie model is introduced for model comparison and its additional material parameter k is found to not be a constant and its usage is discussed. Finally, model comparison and prediction error analysis are used to illustrate the superiority of the proposed damage parameter in multiaxial fatigue life prediction of the two aviation alloys under various loadings.

Fatigue Properties of the Ultra-High Strength Steel TM210A

PubMed Central

Kang, Xia; Zhao, Gui-ping

2017-01-01

This paper presents the results of an experiment to investigate the high cycle fatigue properties of the ultra-high strength steel TM210A. A constant amplitude rotating bending fatigue experiment was performed at room temperature at stress ratio R = −1. In order to evaluate the notch effect, the fatigue experiment was carried out upon two sets of specimens, smooth and notched, respectively. In the experiment, the rotating bending fatigue life was tested using the group method, and the rotating bending fatigue limit was tested using the staircase method at 1 × 107 cycles. A double weighted least square method was then used to fit the stress-life (S–N) curve. The S–N curves of the two sets of specimens were obtained and the morphologies of the fractures of the two sets of specimens were observed with scanning electron microscopy (SEM). The results showed that the fatigue limit of the smooth specimen for rotating bending fatigue was 615 MPa; the ratio of the fatigue limit to tensile strength was 0.29, and the cracks initiated at the surface of the smooth specimen; while the fatigue limit of the notched specimen for rotating bending fatigue was 363 MPa, and the cracks initiated at the edge of the notch. The fatigue notch sensitivity index of the ultra-high strength maraging steel TM210A was 0.69. PMID:28891934

Effects of exercise-induced fatigue on postural balance: a comparison of treadmill versus cycle fatiguing protocols.

PubMed

Wright, Katherine E; Lyons, Thomas S; Navalta, James W

2013-05-01

The authors of this study examined the effects of muscle fatigue on balance indices and recovery time in recreationally trained individuals after incremental tests on a treadmill and a cycle ergometer. Sixteen participants (male N = 11, female N = 5) (mean age = 21.2 ± 2 years) completed this study. Balance measures were performed on a Biodex Balance System via the Dynamic Balance Test. Balance was measured pre-exercise, immediately post-exercise, and at 3-, 6-, 9-, 12-, 15-, 18-, and 21-min post-exercise. Immediately following the fatiguing treadmill test, balance increased significantly in the overall stability index (SI) (from 4.38 ± 2.48 to 6.09 ± 1.80) and the anterior/posterior index (API) (from 3.49 ± 2.18 to 5.28 ± 1.81) (p < 0.01). Immediately following the fatiguing cycle test, balance was not altered significantly in SI or API. Balance was not altered significantly for the medial/lateral index for either exercise test at any time point. Additionally, there were no significant differences in time to recovery. At 12-min post-exercise, all indices were below pre-exercise values, indicating that fatiguing exercise has a positive effect on balance over time. These results are consistent with previous research, suggesting that any effects of fatigue on balance are seen immediately and are diminished as time after exercise increases.

Thermal fatigue testing of a diffusion-bonded beryllium divertor mock-up under ITER-relevant conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Youchison, D.L.; Watson, R.D.; McDonald, J.M.

Thermal response and thermal fatigue tests of four 5-mm-thick beryllium tiles on a Russian Federation International Thermonuclear Experimental Reactor (ITER)-relevant divertor mock-up were completed on the electron beam test system at Sandia National Laboratories. Thermal response tests were performed on the tiles to an absorbed heat flux of 5 MW/m{sup 2} and surface temperatures near 300{degree}C using 1.4 MPa water at 5 m/s flow velocity and an inlet temperature of 8 to 15{degree}C. One tile was exposed to incrementally increasing heat fluxes up to 9.5 MW/m{sup 2} and surface temperatures up to 690{degree}C before debonding at 10MW/m{sup 2}. A secondmore » tile debonded in 25 to 30 cycles at <0.5 MW/m{sup 2}. However, a third tile debonded after 9200 thermal fatigue cycles at 5 MW/m{sup 2}, while another debonded after 6800 cycles. Posttest surface analysis indicated that fatigue failure occurred in the intermetallic layers between the beryllium and copper. No fatigue cracking of the bulk beryllium was observed. It appears that microcracks growing at the diffusion bond produced the observed gradual temperature increases during thermal cycling. These experiments indicate that diffusion-bonded beryllium tiles can survive several thousand thermal cycles under ITER-relevant conditions. However, the reliability of the diffusion-bonded joint remains a serious issue. 17 refs., 25 figs., 6 tabs.« less

Mechanical and low-cycle fatigue behavior of stainless reinforcing steel for earthquake engineering applications

NASA Astrophysics Data System (ADS)

Zhou, Yihui; Ou, Yu-Chen; Lee, George C.; O'Connor, Jerome S.

2010-09-01

Use of stainless reinforcing steel (SRS) in reinforced concrete (RC) structures is a promising solution to corrosion issues. However, for SRS to be used in seismic applications, several mechanical properties need to be investigated. These include specified and actual yield strengths, tensile strengths, uniform elongations and low-cycle fatigue behavior. Three types of SRSs (Talley S24100, Talley 316LN and Talley 2205) were tested and the results are reported in this paper. They were compared with the properties of A706 carbon reinforcing steel (RS), which is typical for seismic applications, and MMFX II, which is a high strength, corrosion resistant RS. Low-cycle fatigue tests of the RS coupons were conducted under strain control with constant amplitude to obtain strain life models of the steels. Test results show that the SRSs have slightly lower moduli of elasticity, higher uniform elongations before necking, and better low-cycle fatigue performance than A706 and MMFX II. All five types of RSs tested satisfy the requirements of the ACI 318 code on the lower limit of the tensile to yield strength ratio. Except Talley 2205, the other four types of RSs investigated meet the ACI 318 requirement that the actual yield strength does not exceed the specified yield strength by more than 18 ksi (124 MPa). Among the three types of SRSs tested, Talley S24100 possesses the highest uniform elongation before necking, and the best low-cycle fatigue performance.

Fatigue crack modeling in bridge deck connection details

DOT National Transportation Integrated Search

1999-12-01

Many steel bridges built prior to 1960 have bridge deck connections that are subject to high cycle fatigue. These connections may be nearing their fatigue limit and will require increased inspection and repair over the next 10 - 20 years. Current ins...

Review of specimen heating in mechanical tests at cryogenic temperatures

NASA Astrophysics Data System (ADS)

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

2014-01-01

At cryogenic temperatures near 4 K, a discontinuous deformation produces a large amount of specimen temperature rise that might bring significant changes in mechanical properties. The authors measured the specimen heating in tensile tests, fatigue test, and other tests in liquid helium for stainless steels and other materials. In this paper, we have measured the specimen temperature in high-cycle and low-cycle fatigue tests for stainless steels at various frequencies and stress levels and evaluated the testing conditions to keep the specimen at a specified temperature. We proposed maximum frequency in load-controlled fatigue tests for specified loading variables and a maximum strain rate in strain-controlled fatigue tests.

Fatigue Life of Bovine Meniscus under Longitudinal and Transverse Tensile Loading

PubMed Central

Creechley, Jaremy J.; Krentz, Madison E.; Lujan, Trevor J.

2017-01-01

The knee meniscus is composed of a fibrous matrix that is subjected to large and repeated loads. Consequently, the meniscus is frequently torn, and a potential mechanism for failure is fatigue. The objective of this study was to measure the fatigue life of bovine meniscus when applying cyclic tensile loads either longitudinal or transverse to the principal fiber direction. Fatigue experiments consisted of cyclic loads to 60, 70, 80 or 90% of the predicted ultimate tensile strength until failure occurred or 20,000 cycles was reached. The fatigue data in each group was fit with a Weibull distribution to generate plots of stress level vs. cycles to failure (S-N curve). Results showed that loading transverse to the principal fiber direction gave a two-fold increase in failure strain, a three-fold increase in creep, and a nearly four-fold increase in cycles to failure (not significant), compared to loading longitudinal to the principal fiber direction. The S-N curves had strong negative correlations between the stress level and the mean cycles to failure for both loading directions, where the slope of the transverse S-N curve was 11% less than the longitudinal S-N curve (longitudinal: S=108–5.9ln(N); transverse: S=112–5.2ln(N)). Collectively, these results suggest that the non-fibrillar matrix is more resistant to fatigue failure than the collagen fibers. Results from this study are relevant to understanding the etiology of atraumatic radial and horizontal meniscal tears, and can be utilized by research groups that are working to develop meniscus implants with fatigue properties that mimic healthy tissue. PMID:28088070

Advanced High Cycle Fatigue (HCF) Life Assurance Methodologies

DTIC Science & Technology

2004-07-01

Fatigue in 2024 - T351 Aluminum Alloy , Wear, 221(1), pp 24-36 (1998) 27. Doner, M., Bain, K.R., and Adams, J.H... alloy , PWA 1484, where temperature and orientation effects both have to be taken into account. Both fracture mechanics and fatigue life methods... effect on predicted fatigue life . On average, the fatigue life is several orders of magnitude less when residual stresses are included. The

Improved High-Cycle Fatigue (HCF) Life Prediction

DTIC Science & Technology

2001-01-01

fatigue in 2024 - T351 aluminum alloy ’, Wear 221, 24-36. Appendix 6C CHARACTERIZATION OF FRETTING FATIGUE INITIATED CRACKS P.J. Golden A.F...0.8. To evaluate the effects of surface residual stresses on notch fatigue life , shot peened specimens were tested at R = -1.0 and 0.1. Data in...Behavior - Response • The undamaged fatigue test program demonstrates the sensitivity of surface effects (for different

Experimental study of crack initiation and propagation in high- and gigacycle fatigue in titanium alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bannikov, Mikhail, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru; Oborin, Vladimir, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru; Naimark, Oleg, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru

Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and SEM to improve methods of monitoring of damage accumulation during fatigue test and to verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both high cycle fatigue andmore » gigacycle fatigue regimes. Fracture surface analysis for plane and cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometer-profiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ∼300 μm has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics.« less

Effects of Stretch Shortening Cycle Exercise Fatigue on Stress Fracture Injury Risk during Landing

ERIC Educational Resources Information Center

James, C. Roger; Dufek, Janet S.; Bates, Barry T.

2006-01-01

The purpose of this study was to examine changes in landing performance during fatigue that could result in increased stress fracture injury risk. Five participants performed nonfatigued and fatigued drop landings (0.60 m), while ground reaction force (GRF), electromyographic (EMG) activity, and kinematics were recorded. Fatigue was defined as a…

A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.

PubMed

Yang, Rui; Arola, Dwayne; Han, Zhihui; Zhang, Xiuyin

2014-10-01

Mechanical and thermal fatigue may affect ceramic restorations in the oral environment. The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics. Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05). Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface. The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Proof test and fatigue crack growth modeling on 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Poe, C. C., Jr.; Dawicke, D. S.

1990-01-01

Pressure proof testing of aircraft fuselage structures has been suggested as a means of screening critical crack sizes and of extending their useful life. The objective of this paper is to study the proof-test concept and to model the crack-growth process on a ductile material. Simulated proof and operational fatigue life tests have been conducted on cracked panels made of 2024-T3 aluminum alloy sheet material. A fatigue crack-closure model was modified to simulate the proof test and operational fatigue cycling. Using crack-growth rate and resistance-curve data, the model was able to predict crack growth during and after the proof load. These tests and analyses indicate that the proof test increases fatigue life; but the beneficial life, after a 1.33 or 1.5 proof, was less than a few hundred cycles.

The effect of temperature on the low cycle fatigue of type 316L stainless steel over the range 20-200°C

NASA Astrophysics Data System (ADS)

Chung, T. E.; Kalantary, M. R.; Faulkner, R. G.; Boutard, J.-L.

1992-09-01

Strain-controlled low cycle fatigue tests (with and without tensile hold) were performed on type 316L stainless steel over the temperature range 20-200°C. The results indicate that for strain ranges of less than 1%, the fatigue life was temperature independent. By contrast, for strain ranges of 1% or more, fatigue life decreased significantly as temperature was increased from 20 to approximately 50°C. It then increased with further increases in temperature until approximately 100°C and beyond when it became relatively temperature insensitive. Fatigue life at all temperatures was reduced with the superimposition of a speak tension hold of 50 s. A model based on the temperature-assisted diffusion of interstitial carbon atoms is proposed to explain the phenomenon.

Docetaxel-related fatigue in men with metastatic prostate cancer: a descriptive analysis.

PubMed

Bergin, A R T; Hovey, E; Lloyd, A; Marx, G; Parente, P; Rapke, T; de Souza, P

2017-09-01

Fatigue is a prevalent and debilitating side effect of docetaxel chemotherapy in metastatic prostate cancer. A better understanding of the kinetics and nature of docetaxel-related fatigue may provide a framework for intervention. This secondary analysis was performed using the MOTIF database, from a phase III, randomised, double-blind, placebo-controlled study of modafinil (200 mg/day for 15 days) for docetaxel-related fatigue in men with metastatic prostate cancer [1]. The pattern of fatigue was analysed using the MDASI (MD Anderson Symptom Inventory) score. The impact of modafinil, cumulative docetaxel exposure, age and smoking status on fatigue kinetics were explored. Fatigue-related symptoms were assessed using the SOMA6 (fatigue and related symptoms) subset of the SPHERE (Somatic and Psychological Health Report). Mood was tracked using the short form 36 health survey questionnaire (SF-36). Across four docetaxel cycles, fatigue scores were higher in the first week and decreased over weeks two and three. Whilst men randomised to modafinil had reduced fatigue scores, cumulative docetaxel had little impact. Younger men (55-68 years) had significantly reduced fatigue scores, whereas current and ex-smokers had higher scores. There was no significant change in mood status or haemoglobin across treatment cycles. Men described both 'somnolence' and 'muscle fatigue' contributing significantly to their symptom complex. Assessment and management of docetaxel-related fatigue remains an important challenge. Given the complex, multifactorial nature of fatigue, identification through structured interview and interventions targeted to specific 'at risk' groups may be the most beneficial. Understanding the temporal pattern (kinetics) and nature of fatigue is critical to guide this process.

Tension and compression fatigue response of unnotched 3D braided composites

NASA Technical Reports Server (NTRS)

Portanova, M. A.

1992-01-01

The unnotched compression and tension fatigue response of a 3-D braided composite was measured. Both gross compressive stress and tensile stress were plotted against cycles to failure to evaluate the fatigue life of these materials. Damage initiation and growth was monitored visually and by tracking compliance change during cycle loading. The intent was to establish by what means the strength of a 3-D architecture will start to degrade, at what point will it degrade beyond an acceptable level, and how this material will typically fail.

Texture, microstructure, and fractal features of the low-cycle fatigue failure of the metal in pipeline welded joints

NASA Astrophysics Data System (ADS)

Usov, V. V.; Gopkalo, E. E.; Shkatulyak, N. M.; Gopkalo, A. P.; Cherneva, T. S.

2015-09-01

Crystallographic texture and fracture features are studied after low-cycle fatigue tests of laboratory specimens cut from the base metal and the characteristic zones of a welded joint in a pipeline after its longterm operation. The fractal dimensions of fracture surfaces are determined. The fractal dimension is shown to increase during the transition from ductile to quasi-brittle fracture, and a relation between the fractal dimension of a fracture surface and the fatigue life of the specimen is found.

Quiet Clean Short-haul Experimental Engine (QCSEE) under-the-wing engine composite fan blade design report

NASA Technical Reports Server (NTRS)

Ravenhall, R.; Salemme, C. T.

1977-01-01

A total of 38 quiet clean short haul experimental engine under the wing composite fan blades were manufactured for various component tests, process and tooling, checkout, and use in the QCSEE UTW engine. The component tests included frequency characterization, strain distribution, bench fatigue, platform static load, whirligig high cycle fatigue, whirligig low cycle fatigue, whirligig strain distribution, and whirligig over-speed. All tests were successfully completed. All blades planned for use in the engine were subjected to and passed a whirligig proof spin test.

Simulation and experiment of thermal fatigue in the CPV die attach

NASA Astrophysics Data System (ADS)

Bosco, Nick; Silverman, Timothy; Kurtz, Sarah

2012-10-01

FEM simulation and accelerated thermal cycling have been performed for the CPV die attach. Trends in fatigue damage accumulation and equivalent test time are explored and found to be most sensitive to temperature ramp rate. Die attach crack growth is measured through cycling and found to be in excellent agreement with simulations of the inelastic strain energy accumulated. Simulations of an entire year of weather data provides for the relative ranking of fatigue damage between four cities as well as their equivalent accelerated test time.

The Effect of Autoclave Sterilization on Resistance to Cyclic Fatigue of Hero Endodontic File #642 (6%) at Two Artificial Curvature.

PubMed

Khabiri, Masoud; Ebrahimi, Maziar; Saei, Mohammad Reza

2017-12-01

File fracture can interfere with cleaning and shaping of the canal and compromise periradicular healing. Autoclave sterilization may prone the files to fracture. The purpose of the present study was to determine the effect of autoclave sterilization on the cyclic fatigue resistance of Hero642 rotary instrument in two curvatures of 45 and 60 degrees. For this experimental in-vitro study, 90 Nickel-Titanium HERO 642 rotary files #30 with 0.06 taper were selected. They were divided into two groups (curvature of 45 and 60 degree) of 45 files. Each group was then subdivided into 3 subgroups; group I: no sterilization, group II: 5 cycles of sterilization and group III: 10 cycles of sterilization. Files were used in artificial canals until fracture. The cyclic fatigue was measured as the number of cycles before fracture. The data was statically analyzed by Student's t-test and two-way analysis of variance. There was a significant difference in cyclic fatigue of two curvature of 45 and 60 degrees ( p = 0.001). However, sterilization process has no significant effect on cyclic fatigue of HERO files ( p = 0.557). Sterilization had no effect on the cyclic fatigue of HERO 642 files when used in curvature of 45 or 60 degrees.

Fatigue of LiNi0.8Co0.15Al0.05O2 in commercial Li ion batteries

NASA Astrophysics Data System (ADS)

Kleiner, Karin; Dixon, Ditty; Jakes, Peter; Melke, Julia; Yavuz, Murat; Roth, Christina; Nikolowski, Kristian; Liebau, Verena; Ehrenberg, Helmut

2015-01-01

The degradation of LiNi0.8Co0.15Al0.05O2 (LNCAO), a cathode material in lithium-ion-batteries, was studied using in situ powder diffraction and in situ Ni K edge X-ray absorption spectroscopy (XAS). The fatigued material was taken from a 7 Ah battery which was cycled for 34 weeks under defined durability conditions. Meanwhile, a cell was stored, as reference, under controlled conditions without electrochemical treatment. The fatigued LNCAO used in this study showed a capacity loss of 26% ± 9% compared to the non-cycled material. During charge and discharge the local and the overall structure of LNCAO was investigated by X-ray near edge structure (XANES) analysis, the extended X-ray absorption fine structure (EXAFS) analysis and by using Rietveld refinement of in situ powder diffraction patterns. Both powder diffraction and XAS revealed additional, rhombohedral phases which do not change with electrochemical cycling. Moreover, a phase with the lattice parameters of fully lithiated LNCAO was still present in the fatigued material at high potentials, while it was absent in the non-fatigued reference material. The coexistence of these phases is described by domains within the LNCAO particles, in correlation with the observed fatigue.

Analysis of fatigue on surface course using dissipated energy approach

NASA Astrophysics Data System (ADS)

Michael; Setyawan, A.; Pramesti, F. P.

2018-03-01

As an important transportation infrastructure, pavement is subjected to repeated vehicle loads that may cause fatigue, which often leads to cracking. The point when this cracking initiates can be determined from the energy dissipated during the loading. This research investigates fatigue in Adi Soemarmo Airport mix-design using bitumen Pen 60/70 + EVA (Ethyl Vinyl Acetate) polymer. An Indirect Tensile Fatigue Test (ITFT) was conducted using stress-controlled loading mode to determine its fatigue life. The stress levels were 500, 600, and 700 kPa, while the loading frequency and the temperature were 10 Hz and 20°C, respectively. The test exhibits strain levels for each loading cycle, which were used to determine the dissipated energy (DE). The result indicates that the DE increases when the number of loading cycles increases, due to progress of the strain levels. The values of DE are 7122.8, 8614.3, and 2654.9 J/m3 for loading levels of 500, 600, and 700 kPa, respectively, whereas the failure points for stress levels of 500, 600, and 700 kPa are 8171, 5161, and 841 cycles, respectively. Thus, the longer the time until the pavement failure point is reached (fatigue life), the greater the amount of energy that is dissipated.

Estimation of fatigue life using electromechanical impedance technique

NASA Astrophysics Data System (ADS)

Lim, Yee Yan; Soh, Chee Kiong

2010-04-01

Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.

Fatigue crack modeling in bridge deck connection details : final report.

DOT National Transportation Integrated Search

1999-12-01

Many steel bridges built prior to 1960 have bridge deck connections that are subject to high cycle fatigue. These connections may be nearing their fatigue limit and will require increased inspection and repair over the next 10 - 20 years. Current ins...

Mechanical Properties and Seawater Behavior of Nitronic 50 (22Cr-13Ni- 5Mn) Plate

DTIC Science & Technology

1976-01-01

Bal - balance misc - miscellaneous cfh - cubic feet per hour mpy - mils per year c/m - cycles per minute my - millivolts CVN - Charpy V-notch No...High-Cycle Fatigue Specimens F_gure 6 - Drawings; Low-Cycle Fatigue Specimens Figure 7 - Curve; Charpy V-Notch Impact Toughness Versus Temperature...for Nitronic 50 Base Plate FiGure 8 - Curve; Charpy V-Notch Toughness Versus Tempera- ture for Nitrcnic 50 Weldments Figure 9 - Photographs; Fracture

Influence of dental restorations and mastication loadings on dentine fatigue behaviour: Image-based modelling approach.

PubMed

Vukicevic, Arso M; Zelic, Ksenija; Jovicic, Gordana; Djuric, Marija; Filipovic, Nenad

2015-05-01

The aim of this study was to use Finite Element Analysis (FEA) to estimate the influence of various mastication loads and different tooth treatments (composite restoration and endodontic treatment) on dentine fatigue. The analysis of fatigue behaviour of human dentine in intact and composite restored teeth with root-canal-treatment using FEA and fatigue theory was performed. Dentine fatigue behaviour was analysed in three virtual models: intact, composite-restored and endodontically-treated tooth. Volumetric change during the polymerization of composite was modelled by thermal expansion in a heat transfer analysis. Low and high shrinkage stresses were obtained by varying the linear shrinkage of composite. Mastication forces were applied occlusally with the load of 100, 150 and 200N. Assuming one million cycles, Fatigue Failure Index (FFI) was determined using Goodman's criterion while residual fatigue lifetime assessment was performed using Paris-power law. The analysis of the Goodman diagram gave both maximal allowed crack size and maximal number of cycles for the given stress ratio. The size of cracks was measured on virtual models. For the given conditions, fatigue-failure is not likely to happen neither in the intact tooth nor in treated teeth with low shrinkage stress. In the cases of high shrinkage stress, crack length was much larger than the maximal allowed crack and failure occurred with 150 and 200N loads. The maximal allowed crack size was slightly lower in the tooth with root canal treatment which induced somewhat higher FFI than in the case of tooth with only composite restoration. Main factors that lead to dentine fatigue are levels of occlusal load and polymerization stress. However, root canal treatment has small influence on dentine fatigue. The methodology proposed in this study provides a new insight into the fatigue behaviour of teeth after dental treatments. Furthermore, it estimates maximal allowed crack size and maximal number of cycles for a specific case. Copyright © 2015 Elsevier Ltd. All rights reserved.

Low-cycle fatigue testing methods

NASA Technical Reports Server (NTRS)

Lieurade, H. P.

1978-01-01

The good design of highly stressed mechanical components requires accurate knowledge of the service behavior of materials. The main methods for solving the problems of designers are: determination of the mechanical properties of the material after cyclic stabilization; plotting of resistance to plastic deformation curves; effect of temperature on the life on low cycle fatigue; and simulation of notched parts behavior.

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

NASA Technical Reports Server (NTRS)

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

1976-01-01

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

High temperature, low-cycle fatigue of copper-base alloys in argon. Part 1: Preliminary results for 12 alloys at 1000 F (538 C)

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

Short-term tensile evaluations at room temperature and 538 C and low-cycle fatigue evaluations at 538 C are presented for the following materials: Zirconium copper-annealed, Zirconium copper-1/4 hard, Zirconium copper-1/2 hard, Tellurium copper-1/2 hard, Chromium copper-SA and aged, OFHC copper-hard, OFHC copper-1/4 hard, OFHC copper-annealed, Silver-as drawn, Zr-Cr-Mg copper-SA, CW and aged, Electroformed copper-30-35 ksi, and Co-Be-Zr- copper-SA, aged. A total of 50 tensile tests and 76 low-cycle fatigue tests were performed using a strain rate of 0.2 percent per second.

Fatigue delamination onset prediction in tapered composite laminates

NASA Technical Reports Server (NTRS)

Murri, Gretchen Bostaph; Salpekar, Satish A.; Obrien, T. Kevin

1989-01-01

Tapered (0 deg) laminates of S2/CE9000 and S2/SP250 glass/epoxies, and IM6/1827I graphite/epoxy were tested in cyclic tension. The specimens usually showed some initial stable delaminations in the tapered region, but these did not affect the stiffness of the specimens, and loading was continued until the specimens either delaminated unstably, or reached 10(exp 6) to 2 x 10(exp 7) million cycles with no unstable delamination. The final unstable delamination originated at the junction of the thin and tapered regions. A finite-element model was developed for the tapered laminate with and without the initial stable delaminations observed in the tests. The analysis showed that for both cases the most likely place for an opening (Mode 1) delamination to originate is at the junction of the taper and thin regions. For each material type, the models were used to calculate the strain energy release rate, G, associated with delaminations originating at that junction and growing either into the thin region or tapered region. For the materials tested, cyclic G(sub Imax) values from DCB tests were used with the maximum strain energy release rates calculated from the finite-element analysis to predict the onset of unstable delamination at the junction as a function of fatigue cycles. The predictions were compared to experimental values of maximum cyclic load as a function of cycles to unstable delamination from fatigue tests in tapered laminates. For the IM6/1827I and S2/SP250 laminates, the predictions agreed very well with the test data. Predicted values for the S2/CE9000 were conservative compared to the test data.

Thermal fatigue and oxidation data for alloy/braze combinations

NASA Technical Reports Server (NTRS)

Hill, V. L.; Humphreys, V. E.

1977-01-01

Thermal fatigue and oxidation data were obtained for 62 brazed specimens of 3 iron-, 3 nickel-, and 1 cobalt-base alloy. Fluidized bed thermal cycling was conducted over the range 740/25 C employing 10 cm long single-edge wedge specimens. Immersion time was always 4 minutes in each bed. Types of test specimens employed in the program include those with brazed overlays on the specimen radius, those butt brazed at midspan and those with a brazed foil overlay on the specimen radius. Of the 18 braze overlay specimens, 5 generated fatigue cracks by 7000 cycles. Thermal cracking of butt brazed specimens occurred exclusively through the butt braze. Of the 23 butt brazed specimens, 7 survived 11,000 thermal cycles without cracking. Only 2 of the 21 foil overlaid specimens exhibiting cracking in 7,000 cycles. Blistering of the foil did occur for 2 alloys by 500 cycles. Oxidation of the alloy/braze combination was limited at the test maximum test temperature of 740 C.

Virtex-5 CN Package Daisy Chain Evaluation Test Report

NASA Technical Reports Server (NTRS)

Suh, Jong-ook

2016-01-01

The board-level temperature cycling reliability of Xilinx Virtex-5 (V5) CN package was investigated. V5s were temperature cycled under two conditions, 0 to +100 C (0/100) and -55 to +100 C (-55/100). During the 0/100 test, no part out of 8 parts failed up to 6586 cycles. During the -55/100 test, one part out of 8 parts failed at 1236 cycle, and there were no additional failures up to 1705 cycles. The failure mode of the part that failed at 1236 cycles indicated that most likely the failure was not a solder fatigue failure, and therefore no obvious solder fatigue failure was observed throughout the tests.

Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene

NASA Astrophysics Data System (ADS)

Zhang, Hanyin; Cai, Linlin; Golub, Michael; Zhang, Yi; Yang, Xuehui; Schlarman, Kate; Zhang, Jing

2018-01-01

Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young's modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 N√ m, the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

Strength, Fatigue, and Fracture Toughness of Ti-6Al-4V Liner from a Composite Over-Wrapped Pressure Vessel

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Lerch, Brad; Thesken, John C.; Sutter, Jim; Russell, Richard

2008-01-01

It was demonstrated by way of experiment that Composite Over-wrapped Pressure Vessel (COPV) Ti-6Al-4V liner material can sustain the expected service loads and cycles. The experiments were performed as part of investigations on the residual life of COPV tanks being used in Space Shuttle Orbiters. Measured properties included tensile strength, compressive strength, reversed loading cycles to simulate liner proof strains, and cyclic fatigue loading to demonstrate the ability to sustain 1000 cycles after liner buckling. The liner material came from a salvaged 40 in. Columbia (orbiter 102) tank (SN029), and tensile strength measurements were made on both boss-transition (thick) and membrane regions (thin). The average measured yield strength was 131 ksi in the boss-transition and membrane regions, in good agreement with measurements made on 1970 s vintage forged plate stock. However, Young s modulus was 17.4+/-0.3 Msi, somewhat higher than typical handbook values (approx.16 Msi). The fracture toughness, as estimated from a failed fatigue specimen, was 74 ksi/sq in, in reasonable agreement with standardized measurements made on 1970 s vintage forged plate stock. Low cycle fatigue of a buckled test specimen implied that as-imprinted liners can sustain over 4000 load cycles.

Influence of different temperatures on the thermal fatigue behavior and thermal stability of hot-work tool steel processed by a biomimetic couple laser technique

NASA Astrophysics Data System (ADS)

Meng, Chao; Zhou, Hong; Zhou, Ying; Gao, Ming; Tong, Xin; Cong, Dalong; Wang, Chuanwei; Chang, Fang; Ren, Luquan

2014-04-01

Three kinds of biomimetic non-smooth shapes (spot-shape, striation-shape and reticulation-shape) were fabricated on the surface of H13 hot-work tool steel by laser. We investigated the thermal fatigue behavior of biomimetic non-smooth samples with three kinds of shapes at different thermal cycle temperature. Moreover, the evolution of microstructure, as well as the variations of hardness of laser affected area and matrix were studied and compared. The results showed that biomimetic non-smooth samples had better thermal fatigue behavior compared to the untreated samples at different thermal cycle temperatures. For a given maximal temperature, the biomimetic non-smooth sample with reticulation-shape had the optimum thermal fatigue behavior, than with striation-shape which was better than that with the spot-shape. The microstructure observations indicated that at different thermal cycle temperatures the coarsening degrees of microstructures of laser affected area were different and the microstructures of laser affected area were still finer than that of the untreated samples. Although the resistance to thermal cycling softening of laser affected area was lower than that of the untreated sample, laser affected area had higher microhardness than the untreated sample at different thermal cycle temperature.

Investigation of a ceramic matrix composite under strain controlled fatigue condition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gudaitis, J.J.; Mall, S.

The fatigue behavior along with damage mechanisms and failure modes of a fiber reinforced ceramic matrix composite with a cross-ply lay-up was investigated under strain controlled mode. Two fatigue conditions involving tension-tension and tension-compression cycling were employed. The strain range versus fatigue life curves for both fatigue conditions were in agreement with each other. However, damage mechanisms and failure modes were different for both cases.

The Relationship of Exercise to Fatigue and Quality of Life in Women With Breast Cancer

DTIC Science & Technology

1999-08-01

exercise study during the first 3 cycles of chemotherapy. Weight change, body mass index, anorexia, nausea, caloric expenditure during exercise and... caloric expenditure increased, fatigue declined. However, the effects of exercise intensity were only significant for the least fatigue (p=.0402) and...Exercise dose and fatigue 25 Table 7. Least squares means and standard errors for four measures of daily fatigue by caloric expenditure . Caloric

The thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies

NASA Technical Reports Server (NTRS)

1982-01-01

The effects of welding, five selected surface coatings, and stress relieving on the thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies were studied using eleven thermal fatigue specimens. Stress relieving was conducted after each 5,000 cycle interval at 1050 F for three hours. Four thermal fatigue specimens were welded with H-13 or maraging steel welding rods at ambient and elevated temperatures and subsequently, subjected to different post-weld heat treatments. Crack patterns were examined at 5,000, 10,000, and 15,000 cycles. The thermal fatigue resistance is expressed by two crack parameters which are the average maximum crack and the average cracked area. The results indicate that a significant improvement in thermal fatigue resistance over the control was obtained from the stress-relieving treatment. Small improvements were obtained from the H-13 welded specimens and from a salt bath nitrogen and carbon-surface treatment. The other surface treatments and welded specimens either did not affect or had a detrimental influence on the thermal fatigue properties of the H-13 die steel.

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

NASA Astrophysics Data System (ADS)

Skorobogatykh, V. N.; Kunavin, S. A.; Prudnikov, D. A.; Shchenkova, I. A.; Bazhenov, A. M.; Zadoinyi, V. A.; Starkovskii, G. L.

2018-02-01

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up-cooling down, opening-closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 103 cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.

Polarization fatigue in ferroelectric Pb(Zr0.52Ti0.48)O3-SrBi2Nb2O9 ceramics

NASA Astrophysics Data System (ADS)

Namsar, Orapim; Pojprapai, Soodkhet; Watcharapasorn, Anucha; Jiansirisomboon, Sukanda

2015-09-01

Ferroelectric fatigue induced by cyclic electric loading of the (1- x)PZT- xSBN ceramics (0.1 ≤ x ≤ 0.3) have been investigated in comparison with pure PZT and SBN ceramics. The results showed that pure PZT ceramic possessed severe polarization fatigue after long bipolar switching pulses. This was mainly attributed to the appearance of microstructural damage at the near-electrode regions. Whereas, pure SBN ceramic exhibited no fatigue at least up to 1 × 106 switching cycles. The fatigue-free behavior of SBN ceramics was due primarily to weak domain wall pinning. PZT-SBN ceramics showed less polarization fatigue up to 1 × 106 switching cycles than pure PZT. This could be attributed to their low oxygen vacancy concentration. Therefore, this new ceramic PZT-SBN system seems to be an alternative material for replacing PZT in ferroelectric memory applications. [Figure not available: see fulltext.

Novel Electrochemical Test Bench for Evaluating the Functional Fatigue Life of Biomedical Alloys

NASA Astrophysics Data System (ADS)

Ijaz, M. F.; Dubinskiy, S.; Zhukova, Y.; Korobkova, A.; Pustov, Y.; Brailovski, V.; Prokoshkin, S.

2017-08-01

The aim of the present work was first to develop and validate a test bench that simulates the in vitro conditions to which the biomedical implants will be actually subjected in vivo. For the preliminary application assessments, the strain-controlled fatigue tests of biomedically pure Ti and Ti-Nb-Zr alloy in simulated body fluid were undertaken. The in situ open-circuit potential measurements from the test bench demonstrated a strong dependence on the dynamic cycling and kind of material under testing. The results showed that during fatigue cycling, the passive oxide film formed on the surface of Ti-Nb-Zr alloy was more resistant to fatigue degradation when compared with pure Ti. The Ti-Nb-Zr alloy exhibited prolonged fatigue life when compared with pure Ti. The fractographic features of both materials were also characterized using scanning electron microscopy. The electrochemical results and the fractographic evidence confirmed that the prolonged functional fatigue life of the Ti-Nb-Zr alloy is apparently ascribable to the reversible martensitic phase transformation.

Interference-Fit-Fastener Investigation

DTIC Science & Technology

1975-09-01

Crack Initiation . .*. . . .* e . . .*. . . .*. 20 Figure 9. Actual and Predicted Fatigue Life Behavior of Notched Open Hole Plates for 2024 - T351 ... Aluminum (Reference 19) * .. . . . . . . . .. . 22 Figure 10. Gage I Strain Response With Cycles . . . . . . . . 24 Figure 11. Fatigue Damage - Life ... Fatigue Behavior", Effect of Environment and Complex Load History on Fatigue Life , ASTM STP 462, pp 74-91 (1970). (7) Grosskreutz, J. C., and Shaw, G. G

Axial and Torsional Load-Type Sequencing in Cumulative Fatigue: Low Amplitude Followed by High Amplitude Loading

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

2001-01-01

The experiments described herein were performed to determine whether damage imposed by axial loading interacts with damage imposed by torsional loading. This paper is a follow on to a study that investigated effects of load-type sequencing on the cumulative fatigue behavior of a cobalt base superalloy, Haynes 188 at 538 C Both the current and the previous study were used to test the applicability of cumulative fatigue damage models to conditions where damage is imposed by different loading modes. In the previous study, axial and torsional two load level cumulative fatigue experiments were conducted, in varied combinations, with the low-cycle fatigue (high amplitude loading) applied first. In present study, the high-cycle fatigue (low amplitude loading) is applied initially. As in the previous study, four sequences (axial/axial, torsion/torsion, axial/torsion, and torsion/axial) of two load level cumulative fatigue experiments were performed. The amount of fatigue damage contributed by each of the imposed loads was estimated by both the Palmgren-Miner linear damage rule (LDR) and the non-linear damage curve approach (DCA). Life predictions for the various cumulative loading combinations are compared with experimental results.

Effect of HIP temperature on microstructure and low cycle fatigue strength of CuCrZr alloy

NASA Astrophysics Data System (ADS)

Nishi, Hiroshi; Enoeda, Mikio

2011-10-01

In order to investigate the effect of the HIP cycle temperatures on the metallurgic degradation and the mechanical properties of CuCrZr alloy, assessments of the microstructure, tensile test, Charpy impact test and low cycle fatigue test are performed for various heat treated CuCrZr alloys, which were solution-annealed followed by water-quenched and aged state of CuCrZr with simulated HIP cycle at temperatures of 980 and 1045 °C. Grain growth occurred on 1045 °C HIP CuCrZr, though slightly on 980 °C HIP CuCrZr. Metallurgic degradation such as voids was not found by optical and SEM observations. There were coarse precipitates in all the CuCrZr and the precipitates did not easily dissolve at 980 °C. The low cycle fatigue strength of 1045 °C HIP CuCrZr was lower than that of other CuCrZr because of the metallurgic degradation caused by the heat cycle, while that of other CuCrZr was corresponding to the best fit curve of ITER MPH.

Complete mechanical characterization of an external hexagonal implant connection: in vitro study, 3D FEM, and probabilistic fatigue.

PubMed

Prados-Privado, María; Gehrke, Sérgio A; Rojo, Rosa; Prados-Frutos, Juan Carlos

2018-06-11

The aim of this study was to fully characterize the mechanical behavior of an external hexagonal implant connection (ø3.5 mm, 10-mm length) with an in vitro study, a three-dimensional finite element analysis, and a probabilistic fatigue study. Ten implant-abutment assemblies were randomly divided into two groups, five were subjected to a fracture test to obtain the maximum fracture load, and the remaining were exposed to a fatigue test with 360,000 cycles of 150 ± 10 N. After mechanical cycling, all samples were attached to the torque-testing machine and the removal torque was measured in Newton centimeters. A finite element analysis (FEA) was then executed in ANSYS® to verify all results obtained in the mechanical tests. Finally, due to the randomness of the fatigue phenomenon, a probabilistic fatigue model was computed to obtain the probability of failure associated with each cycle load. FEA demonstrated that the fracture corresponded with a maximum stress of 2454 MPa obtained in the in vitro fracture test. Mean life was verified by the three methods. Results obtained by the FEA, the in vitro test, and the probabilistic approaches were in accordance. Under these conditions, no mechanical etiology failure is expected to occur up to 100,000 cycles. Graphical abstract ᅟ.

Effects of Control Mode and R-Ratio on the Fatigue Behavior of a Metal Matrix Composite

NASA Technical Reports Server (NTRS)

2005-01-01

Composite Because of their high specific stiffness and strength at elevated temperatures, continuously reinforced metal matrix composites (MMC's) are under consideration for a future generation of aeropropulsion systems. Since components in aeropropulsion systems experience substantial cyclic thermal and mechanical loads, the fatigue behavior of MMC's is of great interest. Almost without exception, previous investigations of the fatigue behavior of MMC's have been conducted in a tension-tension, load-controlled mode. This has been due to the fact that available material is typically less than 2.5-mm thick and, therefore, unable to withstand high compressive loads without buckling. Since one possible use of MMC's is in aircraft skins, this type of testing mode may be appropriate. However, unlike aircraft skins, most engine components are thick. In addition, the transient thermal gradients experienced in an aircraft engine will impose tension-compression loading on engine components, requiring designers to understand how the MMC will behave under fully reversed loading conditions. The increased thickness of the MMC may also affect the fatigue life. Traditionally, low-cycle fatigue (LCF) tests on MMC's have been performed in load control. For monolithic alloys, low-cycle fatigue tests are more typically performed in strain control. Two reasons justify this choice: (1) the critical volume from which cracks initiate and grow is generally small and elastically constrained by the larger surrounding volume of material, and (2) load-controlled, low-cycle fatigue tests of monolithics invariably lead to unconstrained ratcheting and localized necking--an undesired material response because the failure mechanism is far more severe than, and unrelated to, the fatigue mechanism being studied. It is unknown if this is the proper approach to composite testing. However, there is a lack of strain-controlled data on which to base any decisions. Consequently, this study addresses the isothermal, LCF behavior of a [0]_32 MMC tested under strain- and load-controlled conditions for both zero-tension and tension-compression loading conditions. These tests were run at 427 C on thick specimens of SiC-reinforced Ti-15-3. For the fully-reversed tests, no difference was observed in the lives between the load- and strain-controlled tests. However, for the zero-tension tests, the strain-controlled tests had longer lives by a factor of 3 in comparison to the load-controlled tests. This was due to the fact that under strain-control the specimens cyclically softened, reducing the cracking potential. In contrast, the load-controlled tests ratcheted toward larger tensile strains leading to an eventual overload of the fibers. Fatigue tests revealed that specimens tested under fully-reversed conditions had lives approximately an order of magnitude longer than for those specimens tested under zero tension. When examined on a strain-range basis, the fully reversed specimens had similar, but still shorter lives than those of the unreinforced matrix material. However, the composite had a strain limitation at short lives because of the limited strain capacity of the brittle ceramic fiber. The composite also suffered at very high lives because of the lack of an apparent fatigue limit in comparison to the unreinforced matrix. The value of adding fibers to the matrix is apparent when the fatigue lives are plotted as a function of stress range. Here, the composite is far superior to the unreinforced matrix because of the additional load-carrying capacity of the fibers.

Fatigue behavior of 5Ni-Cr-Mo-V steel weldments containing fabrication discontinuities

NASA Technical Reports Server (NTRS)

Gill, Steven J.; Hauser, Joseph A., II; Crooker, Thomas W.; Kruse, Brian J.; Menon, Ravi

1988-01-01

The applicability of linear elastic fracture mechanics to characterize the fatigue behavior of high-strength steel weldments containing lack-of-penetration (LOP) and slag/lack-of-fusion (S/LOF) discontinuities is explored. Full penetration, double-V butt welds with reinforcements removed were tested under zero-to-tension axial loading. Various filler metals and welding techniques were used. Both sound welds and welds containing discontinuities were cycled to failure. Where possible, cycles to crack initiation were estimated by strain gage measurements. The fracture mechanics approach was successful in correlating the fatigue lifetimes of specimens containing single LOP discontinuities of varying size. However, the fatigue behavior of specimens containing multiple S/LOF discontinuities proved to be much more complex and difficult to analyze.

Assessment of microalloying effects on the high temperature fatigue behavior of NiAl

NASA Technical Reports Server (NTRS)

Noebe, R. D.; Lerch, B. A.; Rao, K. B. S.

1995-01-01

Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

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

NASA Astrophysics Data System (ADS)

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.

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

PubMed

Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

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. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of fatigue loading on critical current in stainless steel-laminated DI-BSCCO superconducting composite tape

NASA Astrophysics Data System (ADS)

Hojo, M.; Osawa, K.; Adachi, T.; Inoue, Y.; Osamura, K.; Ochiai, S.; Ayai, N.; Hayashi, K.

2010-11-01

Tensile strain tolerance of the critical current in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) composite superconductor is dramatically improved when the tape is laminated with stainless steel. For practical applications, it is important to understand whether this reinforcement by lamination is effective under fatigue loading. In the present study, we carried out fatigue tests in LN2 and measured the critical current at the specific fatigue cycles to clarify the strain tolerance of the critical current in stainless steel-laminated drastically innovative Bi2223 (DI-BSCCO®) tapes. The fatigue tests were carried out using a computer-controlled 10 kN servo-hydraulic fatigue testing machine with a load cell capacity of 2.5 kN. Tests under static loading showed that the irreversible stress at which the critical current is reduced by 1% from the original value (tensile stress at Ic/Ic0 = 0.99) was 315 MPa when measured at unloading state. The present fatigue tests results indicated that the critical current was maintained at over 98% of the original value at unloading state after stress cycles of 106 when the static irreversible stress was selected as the maximum stress under fatigue loading. Thus, laminated DI-BSCCO tapes showed excellent mechanical properties even under fatigue loading.

Group III/IV locomotor muscle afferents alter motor cortical and corticospinal excitability and promote central fatigue during cycling exercise

PubMed Central

Sidhu, Simranjit K.; Weavil, Joshua C.; Mangum, Tyler S.; Jessop, Jacob E.; Richardson, Russell S.; Morgan, David E.; Amann, Markus

2017-01-01

Objective To investigate the influence of group III/IV muscle afferents on the development of central fatigue and corticospinal excitability during exercise. Methods Fourteen males performed cycling-exercise both under control-conditions (CTRL) and with lumbar intrathecal fentanyl (FENT) impairing feedback from leg muscle afferents. Transcranial magnetic- and cervicomedullary stimulation was used to monitor cortical versus spinal excitability. Results While fentanyl-blockade during non-fatiguing cycling had no effect on motor-evoked potentials (MEPs), cervicomedullary-evoked motor potentials (CMEPs) were 13 ± 3% higher (P < 0.05), resulting in a decrease in MEP/CMEP (P < 0.05). Although the pre- to post-exercise reduction in resting twitch was greater in FENT vs. CTRL (−53 ± 3% vs. −39 ± 3%; P < 0.01), the reduction in voluntary muscle activation was smaller (−2 ± 2% vs. −10 ± 2%; P < 0.05). Compared to the start of fatiguing exercise, MEPs and CMEPs were unchanged at exhaustion in CTRL. In contrast, MEPs and MEP/CMEP increased 13 ± 3% and 25 ± 6% in FENT (P < 0.05). Conclusion During non-fatiguing exercise, group III/IV muscle afferents disfacilitate, or inhibit, spinal motoneurons and facilitate motor cortical cells. In contrast, during exhaustive exercise, group III/IV muscle afferents disfacilitate/inhibit the motor cortex and promote central fatigue. Significance Group III/IV muscle afferents influence corticospinal excitability and central fatigue during whole-body exercise in humans. PMID:27866119

Group III/IV locomotor muscle afferents alter motor cortical and corticospinal excitability and promote central fatigue during cycling exercise.

PubMed

Sidhu, Simranjit K; Weavil, Joshua C; Mangum, Tyler S; Jessop, Jacob E; Richardson, Russell S; Morgan, David E; Amann, Markus

2017-01-01

To investigate the influence of group III/IV muscle afferents on the development of central fatigue and corticospinal excitability during exercise. Fourteen males performed cycling-exercise both under control-conditions (CTRL) and with lumbar intrathecal fentanyl (FENT) impairing feedback from leg muscle afferents. Transcranial magnetic- and cervicomedullary stimulation was used to monitor cortical versus spinal excitability. While fentanyl-blockade during non-fatiguing cycling had no effect on motor-evoked potentials (MEPs), cervicomedullary-evoked motor potentials (CMEPs) were 13±3% higher (P<0.05), resulting in a decrease in MEP/CMEP (P<0.05). Although the pre- to post-exercise reduction in resting twitch was greater in FENT vs. CTRL (-53±3% vs. -39±3%; P<0.01), the reduction in voluntary muscle activation was smaller (-2±2% vs. -10±2%; P<0.05). Compared to the start of fatiguing exercise, MEPs and CMEPs were unchanged at exhaustion in CTRL. In contrast, MEPs and MEP/CMEP increased 13±3% and 25±6% in FENT (P<0.05). During non-fatiguing exercise, group III/IV muscle afferents disfacilitate, or inhibit, spinal motoneurons and facilitate motor cortical cells. In contrast, during exhaustive exercise, group III/IV muscle afferents disfacilitate/inhibit the motor cortex and promote central fatigue. Group III/IV muscle afferents influence corticospinal excitability and central fatigue during whole-body exercise in humans. Copyright © 2016 International Federation of Clinical Neurophysiology. All rights reserved.

Variation of the distribution of crack lengths during corrosion fatigue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishihara, S.; Miyao, K.; Shiozawa, K.

1984-07-01

The detailed initiation and growth behaviour of distributed cracks on a specimen surface was investigated during corrosion fatigue. It can be clarified that the changes of the distribution of crack lengths with stress cycling reflect the behaviour of initiation and growth of distributed cracks. The distribution of crack lengths for certain stress cycles could be explained by a statistical calculation which takes into account both the variation of number of cracks during stress cycling and the scatter of crack growth rate.

Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure

NASA Astrophysics Data System (ADS)

Gao, Huai-Ling; Zhu, Yin-Bo; Mao, Li-Bo; Wang, Feng-Chao; Luo, Xi-Sheng; Liu, Yang-Yi; Lu, Yang; Pan, Zhao; Ge, Jin; Shen, Wei; Zheng, Ya-Rong; Xu, Liang; Wang, Lin-Jun; Xu, Wei-Hong; Wu, Heng-An; Yu, Shu-Hong

2016-09-01

Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (~580 mm s-1), and demonstrates complete recovery and small energy dissipation (~0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 106 cycles at 20% strain and 2.5 × 105 cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

NASA Astrophysics Data System (ADS)

Ghosh, Sabita; Prakash, Raghu V.

2013-01-01

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.

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

NASA Astrophysics Data System (ADS)

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

2015-09-01

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

Effects of the Heterogeneity in the Electron Beam Welded Joint on Mechanical Properties of Ti6Al4V Alloy

NASA Astrophysics Data System (ADS)

Liu, Jing; Gao, Xiao-Long; Zhang, Lin-Jie; Zhang, Jian-Xun

2015-01-01

The aim of this investigation was to evaluate the effect of microstructure heterogeneity on the tensile and low cycle fatigue properties of electron beam welded (EBW) Ti6Al4V sheets. To achieve this goal, the tensile and low cycle fatigue property in the EBW joints and base metal (BM) specimens is compared. During the tensile testing, digital image correlation technology was used to measure the plastic strain field evolution within the specimens. The experimental results showed that the tensile ductility and low cycle fatigue strength of EBW joints are lower than that of BM specimens, mainly because of the effect of microstructure heterogeneity of the welded joint. Moreover, the EBW joints exhibit the cyclic hardening behavior during low fatigue process, while BM specimens exhibit the cyclic softening behavior. Compared with the BM specimens with uniform microstructure, the heterogeneity of microstructure in the EBW joint is found to decrease the mechanical properties of welded joint.

Fatigue response of a PZT multilayer actuator under high-field electric cycling with mechanical preload

NASA Astrophysics Data System (ADS)

Wang, Hong; Wereszczak, Andrew A.; Lin, Hua-Tay

2009-01-01

An electric fatigue test system was developed for evaluating the reliability of piezoelectric actuators with a mechanical loading capability. Fatigue responses of a lead zirconate titanate (PZT) multilayer actuator with a platethrough electrode configuration were studied under an electric field (1.7 times that of the coercive field of PZT material) and a concurrent mechanical preload (30.0 MPa). A total of 109 cycles was carried out. Variations in charge density and mechanical strain under the high electric field and constant mechanical loads were observed during the fatigue test. The dc and the first harmonic (at 10 Hz) dielectric and piezoelectric coefficients were subsequently characterized using fast Fourier transformation. Both the dielectric and the piezoelectric coefficients exhibited a monotonic decrease prior to 2.86×108 cycles under certain preloading conditions, and then fluctuated. Both the dielectric loss tangent and the piezoelectric loss tangent also fluctuated after a decrease. The results are interpreted and discussed with respect to domain wall activities, microdefects, and other anomalies.

Solder creep-fatigue interactions with flexible leaded parts

NASA Technical Reports Server (NTRS)

Ross, R. G., Jr.; Wen, L. C.; Mon, G. R.; Jetter, E.

1992-01-01

With flexible leaded parts, the solder-joint failure process involves a complex interplay of creep and fatigue mechanisms. To better understand the role of creep in typical multi-hour cyclic loading conditions, a specialized non-linear finite-element creep simulation computer program has been formulated. The numerical algorithm includes the complete part-lead-solder-PWB system, accounting for strain-rate dependence of creep on applied stress and temperature, and the role of the part-lead dimensions and flexibility that determine the total creep deflection (solder strain range) during stress relaxation. The computer program has been used to explore the effects of various solder creep-fatigue parameters such as lead height and stiffness, thermal-cycle test profile, and part/board differential thermal expansion properties. One of the most interesting findings is the strong presence of unidirectional creep-ratcheting that occurs during thermal cycling due to temperature dominated strain-rate effects. To corroborate the solder fatigue model predictions, a number of carefully controlled thermal-cycle tests have been conducted using special bimetallic test boards.

Fatigue Behavior of IM7/BMI 5250-4 Composite at Room and Elevated Temperatures

DTIC Science & Technology

2015-03-01

to the ancient Egyptians and their use of clay bricks reinforced with straw, but it is most commonly used in steel-reinforce concrete today [5, p...the temperature increases during the first part of the cure cycle, the viscosity of the resin decreases until the resin becomes a fluid. At about 165...C, the viscosity reaches a minimum value then begins to rise. During the hold at 191°C, a continuous cross-linked network is formed. Crosslinking

Random Heterogeneity Scales and Probabilistic Description of the Long-Lifetime Regime of Fatigue (Preprint)

DTIC Science & Technology

2007-06-01

of subsurface mechanism occurring with decreasing stress. Szczepanski, et al . [21] show that this trend continues into the 107 – 109 cycles regime...close to maximum shear, i.e., slip deformation. 10 20 30 40 50 60 1x105 1x106 Microstructure A Microstructure B An gl e of fa ce t n or m al w .r. t...Szczepanski, et al [22] have also identified this as the predominant subsurface crack initiation mechanism at ultrasonic loading frequencies. The

Compression-compression fatigue of selective electron beam melted cellular titanium (Ti-6Al-4V).

PubMed

Hrabe, Nikolas W; Heinl, Peter; Flinn, Brian; Körner, Carolin; Bordia, Rajendra K

2011-11-01

Regular 3D periodic porous Ti-6Al-4V structures intended to reduce the effects of stress shielding in load-bearing bone replacement implants (e.g., hip stems) were fabricated over a range of relative densities (0.17-0.40) and pore sizes (approximately 500-1500 μm) using selective electron beam melting (EBM). Compression-compression fatigue testing (15 Hz, R = 0.1) resulted in normalized fatigue strengths at 10(6) cycles ranging from 0.15 to 0.25, which is lower than the expected value of 0.4 for solid material of the same acicular α microstructure. The three possible reasons for this reduced fatigue lifetime are stress concentrations from closed porosity observed within struts, stress concentrations from observed strut surface features (sintered particles and texture lines), and microstructure (either acicular α or martensite) with less than optimal high-cycle fatigue resistance. 2011 Wiley Periodicals, Inc.

Relation of cyclic loading pattern to microstructural fracture in creep fatigue

NASA Technical Reports Server (NTRS)

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

1983-01-01

Creep-fatigue-environment interaction is discussed using the 'strainrange partitioning' (SRP) framework as a basis. The four generic SRP strainrange types are studied with a view of revealing differences in micromechanisms of deformation and fatigue degradation. Each combines in a different manner the degradation associated with slip-plane sliding, grain-boundary sliding, migration, cavitation, void development and environmental interaction; hence the approch is useful in delineating the relative importance of these mechanisms in the different loadings. Micromechanistic results are shown for a number of materials, including 316 SS, wrought heat resistant alloys, several nickel-base superalloys, and a tantalum base alloy, T-111. Although there is a commonality of basic behavior, the differences are useful in delineation several important principles of interpretation. Some quantitative results are presented for 316 SS, involving crack initiation and early crack growth, as well as the interaction of low-cycle fatigue with high-cycle fatigue.

Effects of Hot Rolling on Low-Cycle Fatigue Properties of Zn-22 wt.% Al Alloy at Room Temperature

NASA Astrophysics Data System (ADS)

Dong, X. H.; Cao, Q. D.; Ma, S. J.; Han, S. H.; Tang, W.; Zhang, X. P.

2016-09-01

The effects of the reduction ratio (RR) on the low-cycle fatigue (LCF) properties of the Zn-22 wt.% Al (Zn-22Al) alloy were investigated. Various grain sizes from 0.68 to 1.13 μm were obtained by controlled RRs. Tensile and LCF tests were carried out at room temperature. Superplasticity and cyclic softening were observed. Strength and ductility of the rolled Zn-22Al alloy increased with the RR, owing to the decrease in its grain size. The RR did not affect the cyclic softening behavior of the alloy. The fatigue life of the alloy decreased with increasing strain amplitude, while the fatigue life first decreased and then increased with increasing RR. The longest fatigue life was observed for the alloy rolled at a RR of 60%. A bilinear Coffin-Manson relationship was observed to hold true for this alloy.

Low-Cycle Fatigue Behavior of Die-Cast Mg Alloy AZ91

NASA Astrophysics Data System (ADS)

Rettberg, Luke; Anderson, Warwick; Jones, J. Wayne

An investigation has been conducted on the influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91. Fatigue lifetimes were determined from total strain-controlled fatigue tests for strain amplitudes of 0.2%, 0.4% and 0.6%, under fully reversed loading at a frequency of 5 Hz. Cyclic stress-strain behavior was determined using incremental step test (IST) methods. Two locations in a prototype casting with different thicknesses and, therefore, solidification rates, microstructure and porosity, were examined. In general., at all total strain amplitudes fatigue life was unaffected by microstructure refinement and was attributed to significant levels of porosity. Cyclic softening and a subsequent increased cyclic hardening rate, compared to monotonic tests, were observed, independent of microstructure. These results, fractography and damage accumulation processes, determined from metallographic sectioning, are discussed.

Prediction of Functional Overreaching From Subjective Fatigue and Readiness to Train After Only 3 Days of Cycling.

PubMed

Ten Haaf, Twan; van Staveren, Selma; Oudenhoven, Erik; Piacentini, Maria F; Meeusen, Romain; Roelands, Bart; Koenderman, Leo; Daanen, Hein A M; Foster, Carl; de Koning, Jos J

2017-04-01

To investigate whether monitoring of easily measurable stressors and symptoms can be used to distinguish early between acute fatigue (AF) and functional overreaching (FOR). The study included 30 subjects (11 female, 19 male; age 40.8 ± 10.8 y, VO 2 max 51.8 ± 6.3 mL · kg -1 · min -1 ) who participated in an 8-d cycling event over 1300 km with 18,500 climbing meters. Performance was measured before and after the event using a maximal incremental test. Subjects with decreased performance after the event were classified as FOR, others as AF. Mental and physical well-being, internal training load, resting heart rate, temperature, and mood were measured daily during the event. Differences between AF and FOR were analyzed using mixed-model ANOVAs. Logistic regression was used to determine the best predictors of FOR after 3 and 6 d of cycling. Fifteen subjects were classified as FOR and 14 as AF (1 excluded). Although total group changes were observed during the event, no differences between AF and FOR were found for individual monitoring parameters. The combination of questionnaire-based changes in fatigue and readiness to train after 3 d cycling correctly predicted 78% of the subjects as AF or FOR (sensitivity = 79%, specificity = 77%). Monitoring changes in fatigue and readiness to train, using simple visual analog scales, can be used to identify subjects likely to become FOR after only 3 d of cycling. Hence, we encourage athlete support staff to monitor not only fatigue but also the subjective integrated mental and physical readiness to perform.

Energy Approach-Based Simulation of Structural Materials High-Cycle Fatigue

NASA Astrophysics Data System (ADS)

Balayev, A. F.; Korolev, A. V.; Kochetkov, A. V.; Sklyarova, A. I.; Zakharov, O. V.

2016-02-01

The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction.

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

NASA Astrophysics Data System (ADS)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

The Rehbinder effect in iron during giga-cycle fatigue loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bannikov, M. V., E-mail: mbannikov@icmm.ru; Naimark, O. B.

The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. Themore » mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.« less

The Rehbinder effect in iron during giga-cycle fatigue loading

NASA Astrophysics Data System (ADS)

Bannikov, M. V.; Naimark, O. B.

2015-10-01

The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

Influence of fatigue time and level on increases in postural sway.

PubMed

Pline, Kevin M; Madigan, Michael L; Nussbaum, Maury A

2006-12-15

The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose - response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.

Subjective and objective evaluation of visual fatigue on viewing 3D display continuously

NASA Astrophysics Data System (ADS)

Wang, Danli; Xie, Yaohua; Yang, Xinpan; Lu, Yang; Guo, Anxiang

2015-03-01

In recent years, three-dimensional (3D) displays become more and more popular in many fields. Although they can provide better viewing experience, they cause extra problems, e.g., visual fatigue. Subjective or objective methods are usually used in discrete viewing processes to evaluate visual fatigue. However, little research combines subjective indicators and objective ones in an entirely continuous viewing process. In this paper, we propose a method to evaluate real-time visual fatigue both subjectively and objectively. Subjects watch stereo contents on a polarized 3D display continuously. Visual Reaction Time (VRT), Critical Flicker Frequency (CFF), Punctum Maximum Accommodation (PMA) and subjective scores of visual fatigue are collected before and after viewing. During the viewing process, the subjects rate the visual fatigue whenever it changes, without breaking the viewing process. At the same time, the blink frequency (BF) and percentage of eye closure (PERCLOS) of each subject is recorded for comparison to a previous research. The results show that the subjective visual fatigue and PERCLOS increase with time and they are greater in a continuous process than a discrete one. The BF increased with time during the continuous viewing process. Besides, the visual fatigue also induced significant changes of VRT, CFF and PMA.

Fatigue and durability of Nitinol stents.

PubMed

Pelton, A R; Schroeder, V; Mitchell, M R; Gong, Xiao-Yan; Barney, M; Robertson, S W

2008-04-01

Nitinol self-expanding stents are effective in treating peripheral artery disease, including the superficial femoral, carotid, and renal arteries. However, fracture occurrences of up to 50% have been reported in some stents after one year. These stent fractures are likely due to in vivo cyclic displacements. As such, the cyclic fatigue and durability properties of Nitinol-based endovascular stents are discussed in terms of an engineering-based experimental testing program. In this paper, the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing are evaluated for application to both stents and stent subcomponents. In particular, displacement-controlled fatigue tests were performed on stent-like specimens processed from Nitinol microtubing. Fatigue data were collected with combinations of simulated oversizing conditions and pulsatile cycles that were identified by computer modeling of the stent that mimic in vivo deformation conditions. These data are analyzed with non-linear finite element computations and are illustrated with strain-life and strain-based constant-life diagrams. The utility of this approach is demonstrated in conjunction with 10 million cycle pulsatile fatigue tests of Cordis SMART Control((R)) Nitinol self-expanding stents to calculate fatigue safety factors and thereby predict in vivo fatigue resistance. These results demonstrate the non-linear constant fatigue-life response of Nitinol stents, whereby, contrary to conventional engineering materials, the fatigue life of Nitinol is observed to increase with increasing mean strain.

Advanced single crystal for SSME turbopumps

NASA Technical Reports Server (NTRS)

Fritzemeier, L. G.

1989-01-01

The objective of this program was to evaluate the influence of high thermal gradient casting, hot isostatic pressing (HIP) and alternate heat treatments on the microstructure and mechanical properties of a single crystal nickel base superalloy. The alloy chosen for the study was PWA 1480, a well characterized, commercial alloy which had previously been chosen as a candidate for the Space Shuttle Main Engine high pressure turbopump turbine blades. Microstructural characterization evaluated the influence of casting thermal gradient on dendrite arm spacing, casting porosity distribution and alloy homogeneity. Hot isostatic pressing was evaluated as a means of eliminating porosity as a preferred fatigue crack initiation site. The alternate heat treatment was chosen to improve hydrogen environment embrittlement resistance and for potential fatigue life improvement. Mechanical property evaluation was aimed primarily at determining improvements in low cycle and high cycle fatigue life due to the advanced processing methods. Statistically significant numbers of tests were conducted to quantitatively demonstrate life differences. High thermal gradient casting improves as-cast homogeneity, which facilitates solution heat treatment of PWA 1480 and provides a decrease in internal pore size, leading to increases in low cycle and high cycle fatigue lives.

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

Fatigue behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP)

Treesearch

Jinghao Li; John F. Hunt; Shaoqin Gong; Zhiyong Cai

2015-01-01

The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress...

Helicopter Fatigue Life Assessment

DTIC Science & Technology

1981-03-01

is made to bring together alternative statistical opinions. 1. INTRODUCTION In almost arn paper on helicopter fatigue (references 1-15) a diagram is...of fatigue life calculations. In the excercise of the A.H.S., mentioned in the introduction the ratios of fatljue life, based on a cycle counting...monitoring. I INTRODUCTION The requirements for the design of structures of United Kingdom Military aeroplanes against fatigue are contained in Aviation

In-pile testing of ITER first wall mock-ups at relevant thermal loading conditions

NASA Astrophysics Data System (ADS)

Litunovsky, N.; Gervash, A.; Lorenzetto, P.; Mazul, I.; Melder, R.

2009-04-01

The paper describes the experimental technique and preliminary results of thermal fatigue testing of ITER first wall (FW) water-cooled mock-ups inside the core of the RBT-6 experimental fission reactor (RIAR, Dimitrovgrad, Russia). This experiment has provided simultaneous effect of neutron fluence and thermal cycling damages on the mock-ups. A PC-controlled high-temperature graphite ohmic heater was applied to provide cyclic thermal load onto the mock-ups surface. This experiment lasted for 309 effective irradiation days with a final damage level (CuCrZr) of 1 dpa in the mock-ups. About 3700 thermal cycles with a heat flux of 0.4-0.5 MW/m 2 onto the mock-ups were realized before the heater fails. Then, irradiation was continued in a non-cycling mode.

Raman spectral markers of collagen denaturation and hydration in human cortical bone tissue are affected by radiation sterilization and high cycle fatigue damage.

PubMed

Flanagan, Christopher D; Unal, Mustafa; Akkus, Ozan; Rimnac, Clare M

2017-11-01

Thermal denaturation and monotonic mechanical damage alter the organic and water-related compartments of cortical bone. These changes can be detected using Raman spectroscopy. However, less is known regarding Raman sensitivity to detect the effects of cyclic fatigue damage and allograft sterilization doses of gamma radiation. To determine if Raman spectroscopic biomarkers of collagen denaturation and hydration are sensitive to the effects of (a) high cycle fatigue damage and (b) 25kGy irradiation. Unirradiated and gamma-radiation sterilized human cortical bone specimens previously tested in vitro under high-cycle (> 100,000 cycles) fatigue conditions at 15MPa, 25MPa, 35MPa, 45MPa, and 55MPa cyclic stress levels were studied. Cortical bone Raman spectral profiles from wavenumber ranges of 800-1750cm -1 and 2700-3800cm -1 were obtained and compared from: a) non-fatigue vs fatigue fracture sites and b) radiated vs. unirradiated states. Raman biomarker ratios 1670/1640 and 3220/2949, which reflect collagen denaturation and organic matrix (mainly collagen)-bound water, respectively, were assessed. One- and two-way ANOVA analyses were utilized to identify differences between groups along with interaction effects between cyclic fatigue and radiation-induced damage. Cyclic fatigue damage resulted in increases in collagen denaturation (1670/1640: 1.517 ± 0.043 vs 1.579 ± 0.021, p < 0.001) and organic matrix-bound water (3220/2949: 0.109 ± 0.012 vs 0.131 ± 0.008, p < 0.001). Organic matrix-bound water increased secondary to 25kGy irradiation (3220/2949: 0.105 ± 0.010 vs 0.1161 ± 0.009, p = 0.003). Organic matrix-bound water was correlated positively with collagen denaturation (r = 0.514, p < 0.001). Raman spectroscopy can detect the effects of cyclic fatigue damage and 25kGy irradiation via increases in organic matrix (mainly collagen)-bound water. A Raman measure of collagen denaturation was sensitive to cyclic fatigue damage but not 25kGy irradiation. Collagen denaturation was correlated with organic matrix-bound water, suggesting that denaturation of collagen to gelatinous form may expose more binding sites to water by unwinding the triple alpha chains. This research may eventually be useful to help identify allograft quality and more appropriately match donors to recipients. Copyright © 2017 Elsevier Ltd. All rights reserved.

Influence of coarsened and rafted microstructures on the thermomechanical fatigue of a Ni-base superalloy

DOE PAGES

Kirka, M. M.; Brindley, K. A.; Neu, R. W.; ...

2015-08-17

The aging of the microstructure of Ni-base superalloys during service is mainly characterized by coarsening and rafting of the γ' precipitates. The influence of these different aged microstructures on thermomechanical fatigue (TMF) under either continuously cycled (CC) and creep-fatigue (CF) was investigated. Three different aged microstructures, generated through accelerated aging and pre-creep treatments, were studied: stress-free coarsened γ', rafted with orientation perpendicular to loading direction (N-raft), and rafted with orientation parallel to loading direction (P-raft). Under most conditions, the aged microstructures were less resistant to TMF than the virgin microstructure; however, there were exceptions. Both stress-free coarsened and N-raft microstructuresmore » resulted in a reduction in TMF life under both CC and CF conditions in comparison to the virgin material. P-raft microstructure also resulted in reduction in TMF life under CC conditions; however, an increase in life over that of the virgin material was observed under CF conditions. Finally, these differences are discussed and hypothesized to be related to the interactions of the dislocations in the γ channels with γ' precipitates.« less

The Effect of Autoclave Sterilization on Resistance to Cyclic Fatigue of Hero Endodontic File #642 (6%) at Two Artificial Curvature

PubMed Central

Khabiri, Masoud; Ebrahimi, Maziar; Saei, Mohammad Reza

2017-01-01

Statement of the Problem: File fracture can interfere with cleaning and shaping of the canal and compromise periradicular healing. Autoclave sterilization may prone the files to fracture. Purpose: The purpose of the present study was to determine the effect of autoclave sterilization on the cyclic fatigue resistance of Hero642 rotary instrument in two curvatures of 45 and 60 degrees. Materials and Method: For this experimental in-vitro study, 90 Nickel-Titanium HERO 642 rotary files #30 with 0.06 taper were selected. They were divided into two groups (curvature of 45 and 60 degree) of 45 files. Each group was then subdivided into 3 subgroups; group I: no sterilization, group II: 5 cycles of sterilization and group III: 10 cycles of sterilization. Files were used in artificial canals until fracture. The cyclic fatigue was measured as the number of cycles before fracture. The data was statically analyzed by Student’s t-test and two-way analysis of variance. Results: There was a significant difference in cyclic fatigue of two curvature of 45 and 60 degrees (p= 0.001). However, sterilization process has no significant effect on cyclic fatigue of HERO files (p= 0.557). Conclusion: Sterilization had no effect on the cyclic fatigue of HERO 642 files when used in curvature of 45 or 60 degrees. PMID:29201971

Corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloys in different storage environments.

PubMed

Zavanelli, R A; Pessanha Henriques, G E; Ferreira, I; De Almeida Rollo, J M

2000-09-01

Removable partial dentures are affected by fatigue because of the cyclic mechanism of the masticatory system and frequent insertion and removal. Titanium and its alloys have been used in the manufacture of denture frameworks; however, preventive agents with fluorides are thought to attack titanium alloy surfaces. This study evaluated, compared, and analyzed the corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloy in different storage environments. For each metal, 33 dumbbell rods, 2.3 mm in diameter at the central segment, were cast in the Rematitan system. Corrosion-fatigue strength test was carried out through a universal testing machine with a load 30% lower than the 0.2% offset yield strength and a combined influence of different environments: in air at room temperature, with synthetic saliva, and with fluoride synthetic saliva. After failure, the number of cycles were recorded, and fracture surfaces were examined with an SEM. ANOVA and Tukey's multiple comparison test indicated that Ti-6Al-4V alloy achieved 21,269 cycles (SD = 8,355) against 19,157 cycles (SD = 3, 624) for the commercially pure Ti. There were no significant differences between either metal in the corrosion-fatigue life for dry specimens, but when the solutions were present, the fatigue life was significantly reduced, probably because of the production of corrosion pits caused by superficial reactions.

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

PubMed

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

2013-12-01

Accelerated fatigue tests with Ti6Al4V were carried out using a 20kHz ultrasonic testing facility to investigate the cyclic deformation behavior in the Very High Cycle Fatigue (VHCF) regime in detail. Beside parameters like the ultrasonic generator power and the displacement of the specimen, a 3D laser scanning vibrometer was used to characterize the oscillation and fatigue behavior of the Ti-alloy. The course of the S-N(f) curve at the stress ratio R=-1 shows a significant decrease of the bearable stress amplitude and a change from surface to subsurface failures in the VHCF regime for more than 10⁷ cycles. Microscopic investigations of the distribution of the α- and β-phase of Ti6Al4V indicate that inhomogeneities in the phase distribution are reasons for the internal crack initiation. High resolution vibrometry was used to visualize the eigenmode of the designed VHCF-specimen at 20 kHz in the initial state and to indicate local changes in the eigenmodes as a result of progressing fatigue damage. Non-contact strain measurements were realized and used to determine the stress amplitude. The determined stress amplitudes were correlated with strain gauge measurements and finite element analysis. Copyright © 2013 Elsevier B.V. All rights reserved.

Post mortem analysis of fatigue mechanisms in LiNi0.8Co0.15Al0.05O2 - LiNi0.5Co0.2Mn0.3O2 - LiMn2O4/graphite lithium ion batteries

NASA Astrophysics Data System (ADS)

Lang, Michael; Darma, Mariyam Susana Dewi; Kleiner, Karin; Riekehr, Lars; Mereacre, Liuda; Ávila Pérez, Marta; Liebau, Verena; Ehrenberg, Helmut

2016-09-01

The fatigue of commercial lithium ion batteries after long-term cycling at two different temperatures and cycling rates is investigated. The cells are opened after cycling and post-mortem analysis are conducted. Two main contributions to the capacity loss of the batteries are revealed. The loss of active lithium leads to a relative shift between anodes and cathodes potentials. A growth of the solid electrolyte interface (SEI) on the anode is determined as well as the formation of lithium fluoride species as an electrolyte decomposition product. Those effects are reinforced by increasing cycling rates from 1C/2C (charge/discharge) to 2C/3C as well as by increasing cycling temperatures from 25 °C to 40 °C. The other contribution to the capacity loss originates from a fatigue of the blended cathodes consisting of LiNi0.5Co0.2Mn0.3O2 (NCM), LiNi0.8Co0.15Al0.05O2 (NCA) and LiMn2O4 (LMO). Phase-specific capacity losses and fatigue mechanisms are identified. The layered oxides tend to form microcracks and reveal changes of the surface structure leading to a worsening of the lithium kinetics. The cathode exhibits a loss of manganese at 40 °C cycling temperature. Cycling at 40 °C instead of 25 °C has the major impact on cathodes capacity loss, while cycling at 2C/3C rates barely influences it.

Effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, G.D.; Ho, B.Ping Hsiao; Wallace, J.F.

1993-02-01

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientation of (0(2),90(2))2S and (90(2),0(2))2S are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposuremore » of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0 deg ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the apparent strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to +85 C, 500 cycles). Mechanical cycling (0 to 50 percent of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue.« less

Effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Ho, Barry Ping Hsiao; Wallace, John F.

1993-01-01

The effects of thermal and mechanical fatigue on the flexural strength of G40-600/PMR-15 cross-ply laminates with ply orientation of (0(2),90(2))2S and (90(2),0(2))2S are examined. The relative importance of shear and tensile stresses is examined by varying the span-to-depth ratios of flexural test specimens from 8 to 45. Acoustic emission signals are measured during the flexural tests in order to monitor the initiation and growth of damage. Optical microscopy is used to examine specimens for resin cracking, delamination, and fiber breaks after testing. Transverse matrix cracks and delaminations occur in all specimens, regardless of ply orientation, span-to-depth ratio, or previous exposure of specimens to thermal and mechanical fatigue. A small amount of fiber tensile fracture occurs in the outer 0 deg ply of specimens with high span-to-depth ratios. Because of the complex failure modes, the flexural test results represent the 'apparent' strengths rather than the true flexural or shear strengths for these cross-ply laminates. Thermal cycling of specimens prior to flexural testing does not reduce the apparent flexural strength or change the mode of failure. However, fewer acoustic events are recorded at all strains during flexural testing of specimens exposed to prior thermal cycling. High temperature thermal cycling (32 to 260 C, 100 cycles) causes a greater reduction in acoustic events than low temperature thermal cycling (-85 to +85 C, 500 cycles). Mechanical cycling (0 to 50 percent of the flexural strength, 100 cycles) has a similar effect, except that acoustic events are reduced only at strains less than the maximum strain applied during flexural fatigue.

Using aggregated single patient (N-of-1) trials to determine the effectiveness of psychostimulants to reduce fatigue in advanced cancer patients: a rationale and protocol.

PubMed

Senior, Hugh Ej; Mitchell, Geoffrey K; Nikles, Jane; Carmont, Sue-Ann; Schluter, Philip J; Currow, David C; Vora, Rohan; Yelland, Michael J; Agar, Meera; Good, Phillip D; Hardy, Janet R

2013-04-23

It is estimated that 29% of deaths in Australia are caused by malignant disease each year and can be expected to increase with population ageing. In advanced cancer, the prevalence of fatigue is high at 70-90%, and can be related to the disease and/or the treatment. The negative impact of fatigue on function (physical, mental, social and spiritual) and quality of life is substantial for many palliative patients as well as their families/carers. This paper describes the design of single patient trials (n-of-1 s or SPTs) of a psychostimulant, methylphenidate hydrochloride (MPH) (5 mg bd), compared to placebo as a treatment for fatigue, with a population estimate of the benefit by the aggregation of multiple SPTs. Forty patients who have advanced cancer will be enrolled through specialist palliative care services in Australia. Patients will complete up to 3 cycles of treatment. Each cycle is 6 days long and has 3 days treatment and 3 days placebo. The order of treatment and placebo is randomly allocated for each cycle. The primary outcome is a reduction in fatigue severity as measured by the Functional Assessment of Cancer Therapy-fatigue subscale (FACIT-F). Secondary outcomes include adverse events, quality of life, additional fatigue assessments, depression and Australian Karnovsky Performance Scale. This study will provide high-level evidence using a novel methodological approach about the effectiveness of psychostimulants for cancer-related fatigue. If effective, the findings will guide clinical practice in reducing this prevalent condition to improve function and quality of life. Australian New Zealand Clinical Trials Registry ACTRN12609000794202.

Microstructure-sensitive plasticity and fatigue modeling of extruded 6061 aluminum alloys

NASA Astrophysics Data System (ADS)

McCullough, Robert Ross

In this study, the development of fatigue failure and stress anisotropy in light weight ductile metal alloys, specifically Al-Mg-Si aluminum alloys, was investigated. The experiments were carried out on an extruded 6061 aluminum alloy. Reverse loading experiments were performed up to a prestrain of 5% in both tension-followed-by-compression and compression-followed-by-tension. The development of isotropic and kinematic hardening and subsequent anisotropy was indicated by the observation of the Bauschinger effect phenomenon. Experimental results show that 6061 aluminum alloy exhibited a slight increase in the kinematic hardening versus applied prestrain. However, the ratio of kinematic-to-isotropic hardening remained near unity. An internal state variable (ISV) plasticity and damage model was used to capture the evolution of the anisotropy for the as-received T6 and partially annealed conditions. Following the stress anisotropy experiments, the same extruded 6061 aluminum alloy was tested under fully reversing, strain-controlled low cycle fatigue at up to 2.5% strain amplitudes and two heat treatment conditions. Observations were made of the development of striation fields up to the point of nucleation at cracked and clustered precipitants and free surfaces through localized precipitant slip band development. A finite element enabled micro-mechanics study of fatigue damage development of local strain field in the presence of hard phases was conducted. Both the FEA and experimental data sets were utilized in the implementation of a multi-stage fatigue model in order to predict the microstructure response, including fatigue nucleation and propagation contributions on the total fatigue life in AA6061. Good correlation between experimental and predicted results in the number of cycles to final failure was observed. The AA6061 material maintained relatively consistent low cycle fatigue performance despite two different heat treatments.

Fatigue during maximal sprint cycling: unique role of cumulative contraction cycles.

PubMed

Tomas, Aleksandar; Ross, Emma Z; Martin, James C

2010-07-01

Maximal cycling power has been reported to decrease more rapidly when performed with increased pedaling rates. Increasing pedaling rate imposes two constraints on the neuromuscular system: 1) decreased time for muscle excitation and relaxation and 2) increased muscle shortening velocity. Using two crank lengths allows the effects of time and shortening velocity to be evaluated separately. We conducted this investigation to determine whether the time available for excitation and relaxation or the muscle shortening velocity was mainly responsible for the increased rate of fatigue previously observed with increased pedaling rates and to evaluate the influence of other possible fatiguing constraints. Seven trained cyclists performed 30-s maximal isokinetic cycling trials using two crank lengths: 120 and 220 mm. Pedaling rate was optimized for maximum power for each crank length: 135 rpm for the 120-mm cranks (1.7 m x s(-1) pedal speed) and 109 rpm for the 220-mm cranks (2.5 m x s(-1) pedal speed). Power was recorded with an SRM power meter. Crank length did not affect peak power: 999 +/- 276 W for the 120-mm crank versus 1001 +/- 289 W for the 220-mm crank. Fatigue index was greater (58.6% +/- 3.7% vs 52.4% +/- 4.8%, P < 0.01), and total work was less (20.0 +/- 1.8 vs 21.4 +/- 2.0 kJ, P < 0.01) with the higher pedaling rate-shorter crank condition. Regression analyses indicated that the power for the two conditions was most highly related to cumulative work (r2 = 0.94) and to cumulative cycles (r2 = 0.99). These results support previous findings and confirm that pedaling rate, rather than pedal speed, was the main factor influencing fatigue. Our novel result was that power decreased by a similar increment with each crank revolution for the two conditions, indicating that each maximal muscular contraction induced a similar amount of fatigue.

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

DTIC Science & Technology

2007-06-23

6 %AI-2%Sn- 4 %Zr- 6 %Mo in the very high cycle regime. The microstructure is a two-phase structure with primary a grains (ap grains) in a transformed [3...aluminum [2], magnesium [3], nickel-based [ 4 ], and titanium [5,6] alloy systems. Fatigue crack initiation is known to consume the majority of fatigue...microstructural neighborhood affects this process. In fatigue studies of alpha + beta titanium alloys, [ 6 -9] cyclic deformation localization is first observed in

Spectrum Fatigue of 7075-T651 Aluminum Alloy under Overloading and Underloading

DTIC Science & Technology

2016-03-15

underload, stress ratio, and environment on fatigue crack growth. Fatigue crack growth tests were conducted with a 7075-T651 aluminum alloy under constant...the UniGrow equation, the variation of crack length with number of loading cycle was predicted. The prediction and the fatigue test life were found to...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 REPORT NO. NAWCADPAX/TIM-2015/282 ii SUMMARY Fatigue tests of 7075-T651

The NASA Lewis Research Center High Temperature Fatigue and Structures Laboratory

NASA Technical Reports Server (NTRS)

Mcgaw, M. A.; Bartolotta, P. A.

1987-01-01

The physical organization of the NASA Lewis Research Center High Temperature Fatigue and Structures Laboratory is described. Particular attention is given to uniaxial test systems, high cycle/low cycle testing systems, axial torsional test systems, computer system capabilities, and a laboratory addition. The proposed addition will double the floor area of the present laboratory and will be equipped with its own control room.

Short-Term Effect of Aerobic Exercise on Symptoms in Multiple Sclerosis and Chronic Fatigue Syndrome

PubMed Central

Paul, Lorna; McFadyen, Angus K.; Marshall-McKenna, Rebecca; Mattison, Paul; Miller, Linda; McFarlane, Niall G.

2014-01-01

Background: This pilot study was conducted to determine whether a 15-minute bout of moderate-intensity aerobic cycling exercise would affect symptoms (pain and fatigue) and function (Timed 25-Foot Walk test [T25FW] and Timed Up and Go test [TUG]) in people with multiple sclerosis (MS) or chronic fatigue syndrome (CFS), and to compare these results with those of a healthy control group. Methods: Eight people with MS (Expanded Disability Status Scale score 5–6; Karnofsky score 50–80), eight people with CFS (Karnofsky score 50–80), and eight healthy volunteers participated in the study. Pain and fatigue levels and results of the T25FW and TUG were established at baseline as well as at 30 minutes, 2 hours, and 24 hours following a 15-minute stationary cycling aerobic exercise test. Repeated-measures analysis of variance (ANOVA) and covariance (ANCOVA) were used to analyze the findings over time. Results: At baseline there were statistically significant differences between groups in fatigue (P = .039), T25FW (P = .034), and TUG (P = .010). A significant group/time interaction emerged for fatigue levels (P= .005). We found no significant group/time interaction for pain levels or function. Conclusions: Undertaking 15 minutes of moderate-intensity aerobic cycling exercise had no significant adverse effects on pain or function in people with MS and CFS (with a Karnofsky score of 50–80) within a 24-hour time period. These initial results suggest that people with MS or CFS may undertake 15 minutes of cycling as moderate aerobic exercise with no expected negative impact on pain or function. PMID:25061431

Interaction of Lamb Waves with Fatigue Cracks in Aluminum

DTIC Science & Technology

2011-09-01

Interaction of Lamb Waves with Fatigue Cracks in Aluminum E. D. SWENSON, C. T. OWENS and C. ALLEN ABSTRACT Elastic waves can travel across...the interaction of Lamb waves with both open and closed low-cycle fatigue cracks in aluminum plates using a three-dimensional laser Doppler vibrometer...and antisymmetric Lamb wave modes differ upon encountering fatigue cracks. INTRODUCTION The use of guided elastic waves (Lamb waves) has shown

Microstructure and fatigue resistance of high strength dual phase steel welded with gas metal arc welding and plasma arc welding processes

NASA Astrophysics Data System (ADS)

Ahiale, Godwin Kwame; Oh, Yong-Jun; Choi, Won-Doo; Lee, Kwang-Bok; Jung, Jae-Gyu; Nam, Soo Woo

2013-09-01

This study presents the microstructure and high cycle fatigue performance of lap shear joints of dual phase steel (DP590) welded using gas metal arc welding (GMAW) and plasma arc welding (PAW) processes. High cycle fatigue tests were conducted on single and double lap joints under a load ratio of 0.1 and a frequency of 20 Hz. In order to establish a basis for comparison, both weldments were fabricated to have the same weld depth in the plate thickness. The PAW specimens exhibited a higher fatigue life, a gentle S-N slope, and a higher fatigue limit than the GMAW specimens. The improvement in the fatigue life of the PAW specimens was primarily attributed to the geometry effect that exhibited lower and wider beads resulting in a lower stress concentration at the weld toe where cracks initiate and propagate. Furthermore, the microstructural constituents in the heat-affected zone (HAZ) of the PAW specimens contributed to the improvement. The higher volume fraction of acicular ferrite in the HAZ beneath the weld toe enhanced the PAW specimen's resistance to fatigue crack growth. The double lap joints displayed a higher fatigue life than the single lap joints without changing the S-N slope.

Crystallographic Analysis of Fatigue Crack Initiation Behavior in Coarse-Grained Magnesium Alloy Under Tension-Tension Loading Cycles

NASA Astrophysics Data System (ADS)

Tamada, Kazuhiro; Kakiuchi, Toshifumi; Uematsu, Yoshihiko

2017-07-01

Plane bending fatigue tests are conducted to investigate fatigue crack initiation mechanisms in coarse-grained magnesium alloy, AZ31, under the stress ratios R = -1 and 0.1. The initial crystallographic structures are analyzed by an electron backscatter diffraction method. The slip or twin operation during fatigue tests is identified from the line angle analyses based on Euler angles of the grains. Under the stress ratio R = -1, relatively thick tension twin bands are formed in coarse grains. Subsequently, compression twin or secondary pyramidal slip operates within the tension twin band, resulting in the fatigue crack initiation. On the other hand, under R = 0.1 with tension-tension loading cycles, twin bands are formed on the specimen surface, but the angles of those bands do not correspond to tension twins. Misorientation analyses of c-axes in the matrix grain and twin band reveal that double twins are activated. Under R = 0.1, fatigue crack initiates along the double twin boundaries. The different manners of fatigue crack initiation at R = -1 and 0.1 are related to the asymmetricity of twining under tension and compression loadings. The fatigue strengths under different stress ratios cannot be estimated by the modified Goodman diagram due to the effect of stress ratio on crack initiation mechanisms.

Synergistic Effects of Temperature, Oxidation and Multicracking Modes on Damage Evolution and Life Prediction of 2D Woven Ceramic-Matrix Composites under Tension-Tension Fatigue Loading

NASA Astrophysics Data System (ADS)

Longbiao, Li

2017-08-01

In this paper, the synergistic effects of temperature, oxidation and multicracking modes on damage evolution and life prediction in 2D woven ceramic-matrix composites (CMCs) have been investigated. The damage parameter of fatigue hysteresis dissipated energy and the interface shear stress were used to monitor the damage evolution inside of CMCs. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface/fiber oxidation model, interface wear model and fibers statistical failure model at elevated temperature, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfy the Global Load Sharing (GLS) criterion. When the broken fibers fraction approaches to the critical value, the composite fatigue fractures. The evolution of fatigue hysteresis dissipated energy, the interface shear stress and broken fibers fraction versus cycle number, and the fatigue life S-N curves of SiC/SiC at 1000, 1200 and 1300 °C in air and steam condition have been predicted. The synergistic effects of temperature, oxidation, fatigue peak stress, and multicracking modes on the evolution of interface shear stress and fatigue hysteresis dissipated energy versus cycle numbers curves have been analyzed.

Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

NASA Astrophysics Data System (ADS)

Hayashi, Morihito; Toeda, Kazunori

In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

Fatigue Crack Prognostics by Optical Quantification of Defect Frequency

NASA Astrophysics Data System (ADS)

Chan, K. S.; Buckner, B. D.; Earthman, J. C.

2018-01-01

Defect frequency, a fatigue crack prognostics indicator, is defined as the number of microcracks per second detected using a laser beam that is scanned across a surface at a constant predetermined frequency. In the present article, a mechanistic approach was taken to develop a methodology for deducing crack length and crack growth information from defect frequency data generated from laser scanning measurements made on fatigued surfaces. The method was developed by considering a defect frequency vs fatigue cycle curve that comprised three regions: (i) a crack initiation regime of rising defect frequency, (ii) a plateau region of a relatively constant defect frequency, and (iii) a region of rapid rising defect frequency due to crack growth. Relations between defect frequency and fatigue cycle were developed for each of these three regions and utilized to deduce crack depth information from laser scanning data of 7075-T6 notched specimens. The proposed method was validated using experimental data of crack density and crack length data from the literature for a structural steel. The proposed approach was successful in predicting the length or depth of small fatigue cracks in notched 7075-T6 specimens and in smooth fatigue specimens of a structural steel.

Microstructural Features Controlling the Variability in Low-Cycle Fatigue Properties of Alloy Inconel 718DA at Intermediate Temperature

NASA Astrophysics Data System (ADS)

Texier, Damien; Gómez, Ana Casanova; Pierret, Stéphane; Franchet, Jean-Michel; Pollock, Tresa M.; Villechaise, Patrick; Cormier, Jonathan

2016-03-01

The low-cycle fatigue behavior of two direct-aged versions of the nickel-based superalloy Inconel 718 (IN718DA) was examined in the low-strain amplitude regime at intermediate temperature. High variability in fatigue life was observed, and abnormally short lifetimes were systematically observed to be due to crack initiation at (sub)-surface non-metallic inclusions. However, crack initiation within (sub)-surface non-metallic inclusions did not necessarily lead to short fatigue life. The macro- to micro-mechanical mechanisms of deformation and damage have been examined by means of detailed microstructural characterization, tensile and fatigue mechanical tests, and in situ tensile testing. The initial stages of crack micro-propagation from cracked non-metallic particles into the surrounding metallic matrix occupies a large fraction of the fatigue life and requires extensive local plastic straining in the matrix adjacent to the cracked inclusions. Differences in microstructure that influence local plastic straining, i.e., the δ-phase content and the grain size, coupled with the presence of non-metallic inclusions at the high end of the size distribution contribute strongly to the fatigue life variability.

Effect of cyclic fatigue on the fracture toughness of Polyoxymethylene

NASA Astrophysics Data System (ADS)

Ramoa, B.; Berer, M.; Schwaiger, M.; Pinter, G.

2017-05-01

Polymers are used in a wide range of applications and their properties are dependent upon the morphological development during processing and the specimen configuration which in turn define the mechanical properties. In this context fatigue and monotonic testing are part of the standard procedure to assess relevant mechanical and material parameters to ensure a better part design. The present work addresses the performance issues of a real component made of Polyoxymethylene (POM) which is subjected to cyclic loads from intermediate levels to high peak values inside a damping mechanism. For this linear elastic fracture mechanics concepts were used to characterize the behavior of a POM homopolymer resin used in this application. Injection molded compact tension specimens, with sharp and blunt notches, were tested under a combination of cyclic and monotonic loads and the fracture surfaces were examined. The critical stress intensity factor obtained by monotonic tests was evaluated as a function of the cycle number, where an increase after the first 1000 cycles followed by a continuous decrease with higher numbers of cycles was observed. A variation of approximately 50% and 70% were obtained along the duration of the tests for the sharp and blunt notch specimens, respectively. In light of the obtained results, a discussion is presented considering the dynamic specimen compliance and the structural features observed on the fracture surfaces in combination with the fracture mechanical response.

Microstructural evaluation of cumulative fatigue damage below the fatigue limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuoka, C.; Nakagawa, Y.G.

1996-05-01

The objective of this work is to evaluate the microstructural changes induced near and below the fatigue limit in a pressure vessel steel plate, SA508. Dislocation cell to cell misorientation differences, {theta}, which increase with fatigue damage accumulation, are measured by the Selected Area Diffraction (SAD) method. The misorientation difference, {theta}, of the sample failed just above the fatigue limit is about 4.0 degrees on the average, which is about the same as that for the failure conditions of low cycle fatigue at higher stresses. The {theta} value increases even below the fatigue limit, but it does not increase atmore » stresses which are lower than 50% of the fatigue limit.« less

High-temperature, low-cycle fatigue of advanced copper-base alloys for rocket nozzles. Part 2: NASA 1.1, Glidcop, and sputtered copper alloys

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1974-01-01

Short-term tensile and low-cycle fatigue data are reported for five advance copper-base alloys: Sputtered Zr-Cu as received, sputtered Zr-Cu heat-treated, Glidcop AL-10, and NASA alloys 1-1A and 1-1B. Tensile tests were performed in argon at 538 C using an axial strain rate of 0.002/sec. Yield strength and ultimate tensile strength data are reported along with reduction in area values. Axial strain controlled low-cycle fatigue tests were performed in argon at 538C using an axial strain rate of 0.002/sec to define the fatigue life over the range from 100 to 3000 cycles for the five materials studied. It was found that the fatigue characteristics of the NASA 1-1A and NASA 1-1B compositions are identical and represent fatique life values which are much greater than those for the other materials tested. The effect of temperature on NASA 1-1B alloy at a strain rate of 0.002/sec was evaluated along with the effect of strain rates of 0.0004 and 0.01/sec at 538 C. Hold-time data are reported for the NASA 1-1B alloy at 538 C using 5 minute hold periods in tension only and compression only at two different strain range values. Hold periods in tension were much more detrimental than hold periods in compression.

An Abnormal Increase of Fatigue Life with Dwell Time during Creep-Fatigue Deformation for Directionally Solidified Ni-Based Superalloy DZ445

NASA Astrophysics Data System (ADS)

Ding, Biao; Ren, Weili; Deng, Kang; Li, Haitao; Liang, Yongchun

2018-03-01

The paper investigated the creep-fatigue behavior for directionally solidified nickel-based superalloy DZ445 at 900 °C. It is found that the fatigue life shows an abnormal increase when the dwell time exceeds a critical value during creep-fatigue deformation. The area of hysteresis loop and fractograph explain the phenomenon quite well. The shortest life corresponds to the maximal area of hysteresis loop, i. e. the maximum energy to be consumed during the creep-fatigue cycle. The fractographic observation of failed samples further supports the abnormal behavior of fatigue life.

The effects of autoclave sterilization on the cyclic fatigue resistance of ProTaper Universal, ProTaper Next, and ProTaper Gold nickel-titanium instruments.

PubMed

Özyürek, Taha; Yılmaz, Koray; Uslu, Gülşah

2017-11-01

It was aimed to compare the cyclic fatigue resistances of ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG) and the effects of sterilization by autoclave on the cyclic fatigue life of nickel-titanium (NiTi) instruments. Eighty PTU, 80 PTN, and 80 PTG were included to the present study. Files were tested in a simulated canal. Each brand of the NiTi files were divided into 4 subgroups: group 1, as received condition; group 2, pre-sterilized instruments exposed to 10 times sterilization by autoclave; group 3, instruments tested were sterilized after being exposed to 25%, 50%, and 75% of the mean cycles to failure, then cycled fatigue test was performed; group 4, instruments exposed to the same experiment with group 3 without sterilization. The number of cycles to failure (NCF) was calculated. The data was statistically analyzed by using one-way analysis of variance and post hoc Tukey tests. PTG showed significantly higher NCF than PTU and PTN in group 1 ( p < 0.05). Sterilization significantly increased the NCF of PTN and PTG ( p < 0.05) in group 2. PTN in group 3 had significantly higher cyclic fatigue resistance than PTN group 4 ( p < 0.05). Also, significantly higher NCF was observed for PTG in group 2 than in groups 3 and 4 ( p < 0.05). PTG instrument made of new gold alloy was more resistant to fatigue failure than PTN and PTU. Autoclaving increased the cyclic fatigue resistances of PTN and PTG.

Experimental evaluation of cyclic fatigue resistance of four different nickel-titanium instruments after immersion in sodium hypochlorite and/or sterilization

PubMed Central

BULEM, Üreyen Kaya; KECECI, Ayse Diljin; GULDAS, Hilmi Egemen

2013-01-01

NiTi instruments have a high risk of separation due to torsional or flexural fatigue (cyclic fatigue). Chemomechanical preparation, cleaning procedures, chemical disinfection and sterilization cause the corrosion of endodontic instruments that may weaken the fracture resistance of the instruments. Objective To assess the effects of NaOCl immersion and autoclave sterilization on the cyclic fatigue resistance of ProFile, FlexMaster, Mtwo and TwistedFiles NiTi instruments (tip size 25, 0.06 taper, n=160). Material and Methods The instruments (n=10 for each subgroup) were dynamically immersed in NaOCl; immersed in NaOCl and sterilized in one autoclave cycle; 5 cycles immersed in NaOCl and sterilized in autoclave and not immersed in NaOCl and not sterilized (control group). Dynamic cyclic fatigue resistance was tested. The number of cycles to failure (NCF) were statistically analyzed (P<0.05). Results Kruskall-Wallis test indicated significant differences among the tested instruments in terms of NCF (P=0.000). The mean NCF of Mtwo (556.75) was higher than that of the Twisted File, Flexmaster and ProFile, 483.1, 376.12, 365.25, respectively. NaOCl immersion and autoclave sterilization have no effect on the NCF values of the tested instruments (P>.05). Conclusions Cyclic fatigue resistance of the tested NiTi instruments cannot be adversely affected by NaOCl immersion and autoclave sterilization. Production process (TwistedFiles) or design (Twisted Files, FlexMaster, Mtwo and ProFile) of the instruments can influence their cyclic fatigue resistance. PMID:24473715

Axial Fatigue Tests at Zero Mean Stress of 24S-T Aluminum-alloy Sheet with and Without a Circular Hole

NASA Technical Reports Server (NTRS)

Brueggeman, W C; Mayer, M JR; Smith, W H

1944-01-01

Axial fatigue tests were made on 189 coupon specimens of 0.032-inch 24S-T aluminum-alloy sheet and a few supplementary specimens of 0.004-inch sheet. The mean load was zero. The specimens were restrained against lateral buckling by lubricated solid guides described in a previous report on this project. About two-thirds of the 0.032-inch specimens were plain coupons nominally free from stress raisers. The remainder contained a 0.1285-inch drilled hole at the center where the reduced section was 0.5 inch wide. S-N diagrams were obtained for cycles to failure between about 1000 and 10 to the 7th power cycles for the plain specimens and 17 and 10 to the 7th power cycles for the drilled specimens. The fatigue stress concentration factor increased from about 1.08 for a stress amplitude causing failure at 0.25 cycles (static) to a maximum of 1.83 at 15,000 cycles and then decreased gradually. The graph for the drilled specimens showed less scatter than that for the plain specimens.

Ultrasonic Fatigue Endurance of Thin Carbon Fiber Sheets

NASA Astrophysics Data System (ADS)

Domínguez Almaraz, Gonzalo M.; Ruiz Vilchez, Julio A.; Dominguez, Aymeric; Meyer, Yann

2016-04-01

Ultrasonic fatigue tests were carried out on thin carbon fiber sheets (0.3 mm of thickness) to determine the fatigue endurance under very high-frequency loading (20 kHz). This material, called the gas diffusion layer (GDL), plays a major role in the overall performances of proton exchange membrane fuel cells (PEMFCs). The study of its physical-chemical properties is an on-going subject in the literature; nevertheless, no knowledge is available concerning the high-frequency fatigue endurance. A principal difficulty in carrying out ultrasonic fatigue tests on this material was to determine the dimensions of testing specimen to fit the resonance condition. This aspect was solved by modal numerical simulation: The testing specimen has been a combination of a low-strength steel frame (to facilitate the attachment to the ultrasonic machine and to increase the mass of the specimen), and the carbon fiber hourglass-shape profile. Under resonance condition, a stationary elastic wave is generated along the specimen that induces high stress at the neck section and high displacements at the ends. Results show that fatigue life was close to 3 × 108 cycles when the high Von Misses stress at the neck section was 170 MPa, whereas fatigue life attains the 4.5 × 109 cycles when stress decreases to 117 MPa. Crack initiation and propagation were analyzed, and conclusions were drawn concerning the fatigue endurance of these fiber carbon sheets under ultrasonic fatigue testing.

Simulation of fatigue crack growth under large scale yielding conditions

NASA Astrophysics Data System (ADS)

Schweizer, Christoph; Seifert, Thomas; Riedel, Hermann

2010-07-01

A simple mechanism based model for fatigue crack growth assumes a linear correlation between the cyclic crack-tip opening displacement (ΔCTOD) and the crack growth increment (da/dN). The objective of this work is to compare analytical estimates of ΔCTOD with results of numerical calculations under large scale yielding conditions and to verify the physical basis of the model by comparing the predicted and the measured evolution of the crack length in a 10%-chromium-steel. The material is described by a rate independent cyclic plasticity model with power-law hardening and Masing behavior. During the tension-going part of the cycle, nodes at the crack-tip are released such that the crack growth increment corresponds approximately to the crack-tip opening. The finite element analysis performed in ABAQUS is continued for so many cycles until a stabilized value of ΔCTOD is reached. The analytical model contains an interpolation formula for the J-integral, which is generalized to account for cyclic loading and crack closure. Both simulated and estimated ΔCTOD are reasonably consistent. The predicted crack length evolution is found to be in good agreement with the behavior of microcracks observed in a 10%-chromium steel.

A wireless body measurement system to study fatigue in multiple sclerosis.

PubMed

Yu, Fei; Bilberg, Arne; Stenager, Egon; Rabotti, Chiara; Zhang, Bin; Mischi, Massimo

2012-12-01

Fatigue is reported as the most common symptom by patients with multiple sclerosis (MS). The physiological and functional parameters related to fatigue in MS patients are currently not well established. A new wearable wireless body measurement system, named Fatigue Monitoring System (FAMOS), was developed to study fatigue in MS. It can continuously measure electrocardiogram, body-skin temperature, electromyogram and motions of feet. The goal of this study is to test the ability of distinguishing fatigued MS patients from healthy subjects by the use of FAMOS. This paper presents the realization of the measurement system including the design of both hardware and dedicated signal processing algorithms. Twenty-six participants including 17 MS patients with fatigue and 9 sex- and age-matched healthy controls were included in the study for continuous 24 h monitoring. The preliminary results show significant differences between fatigued MS patients and healthy controls. In conclusion, the FAMOS enables continuous data acquisition and estimation of multiple physiological and functional parameters. It provides a new, flexible and objective approach to study fatigue in MS, which can distinguish between fatigued MS patients and healthy controls. The usability and reliability of the FAMOS should however be further improved and validated through larger clinical trials.

Evaluation of the resistance to cyclic fatigue among ProTaper Next, ProTaper Universal, and Vortex Blue rotary instruments.

PubMed

Nguyen, Harrison H; Fong, Hanson; Paranjpe, Avina; Flake, Natasha M; Johnson, James D; Peters, Ove A

2014-08-01

The purpose of this study was to compare the fracture resistance to cyclic fatigue of ProTaper Next (PTN; Dentsply Tulsa Dental Specialties, Tulsa, OK), ProTaper Universal (PTU, Dentsply Tulsa Dental Specialties), and Vortex Blue (VB, Dentsply Tulsa Dental Specialties) rotary instruments. Twenty instruments each of PTN X1-X5, PTU S1-F5, and VB 20/04-50/04 were rotated until fracture in a simulated canal of 90° and a 5-mm radius using a custom-made testing platform. The number of cycles to fracture (NCF) was calculated. Weibull analysis was used to predict the maximum number of cycles when 99% of the instrument samples survive. VB 20/04-30/04 had significantly higher NCF than PTU S1-F5 and PTN X1-X5. VB 35/04-45/04 had significantly higher NCF than PTU S2-F5 and PTN X2-X5. PTN X1 had higher NCF than PTU S1-F5. PTN X2 had higher NCF than PTU F2-F5. The Weibull distribution predicted the highest number of cycles at which 99% of instruments survive to be 766 cycles for VB 25/04 and the lowest to be 50 cycles for PTU F2. Under the limitations of this study, VB 20/04-45/04 were more resistant to cyclic fatigue than PTN X2-X5 and PTU S2-F5. PTN X1 and X2 were more resistant to cyclic fatigue than PTU F2-F5. The Weibull distribution appears to be a feasible and potentially clinically relevant model to predict resistance to cyclic fatigue. Copyright © 2014 American Association of Endodontists. All rights reserved.

Effect of cyclic conditions on the dynamic oxidation of gas turbine superalloys

NASA Technical Reports Server (NTRS)

Johnston, J. R.; Ashbrook, R. L.

1974-01-01

The effects of operating parameters of a dynamic apparatus used to study oxidation and thermal fatigue of gas turbine materials were studied. IN-100, TD-NiCr, and WI-52 were tested at a maximum temperature of 1,090 deg C. Heating time per cycle was varied from 1/20 hr to 10 hr. Minimum temperatures between heating cycles were room temperature, 430 deg, and 650 deg C. Cooling air velocities were zero, Mach 0.7, and Mach 1. Increasing the number of cycles for a given time at temperature increased weight loss. Thermal fatigue was related to number of cycles more than to time at temperature.

Tiered deposition of sub-5 nm ferroelectric Hf1-xZrxO2 films on metal and semiconductor substrates

NASA Astrophysics Data System (ADS)

Walters, Glen; Shekhawat, Aniruddh; Rudawski, Nicholas G.; Moghaddam, Saeed; Nishida, Toshikazu

2018-05-01

Using a tiered deposition approach, Hf1-xZrxO2 (HZO) films with varying atomic layer deposition (ALD) cycles from 36 to 52 cycles were grown on Ge, Ir, and TiN substrates in single runs and annealed at 500 °C. 40 ALD cycle films grown on Ir exhibit a switched polarization (Psw) of 13 μC/cm2, while those grown on Ge and TiN did not exhibit measurable Psw values until 44 and 52 ALD cycles, respectively. High-resolution cross-sectional transmission electron microscopy confirmed these results; the ferroelectric films are crystalline with defined lattice fringes, while non-ferroelectric films remain amorphous. 52 ALD cycle 1:1 HZO grown on Ge had the highest Psw of all the films fabricated at 39 μC/cm2, while the 1:1 HZO grown on TiN displayed continuous wake-up and no fatigue up to 1010 cycles with the Psw increasing from <1 μC/cm2 to 21 μC/cm2.

The effects of novel surface treatments on the wear and fatigue properties of steel and chilled cast iron

NASA Astrophysics Data System (ADS)

Carroll, Jason William

Contact fatigue driven wear is a principal design concern for gear and camshaft engineering of power systems. To better understand how to engineer contact fatigue resistant surfaces, the effects of electroless nickel and hydrogenated diamond-like-carbon (DLC) coatings on the fatigue life at 108 cycles of SAE 52100 steel were studied using ultrasonic fatigue methods. The addition of DLC and electroless nickel coatings to SAE 52100 bearing steel had no effect on the fatigue life. Different inclusion types were found to affect the stress intensity value beyond just the inclusion size, as theorized by Murakami. The difference in stress intensity values necessary to propagate a crack for Ti (C,N) and alumina inclusions was due to the higher driving force for crack extension at the Ti (C,N) inclusions and was attributed to differences in the shape of the inclusion: rhombohedral for the Ti (C,N) versus spherical for the oxides. A correction factor was added to the Murakami equation to account for inclusion type. The wear properties of DLC coated SAE 52100 and chilled cast iron were studied using pin-on-disk tribometry and very high cycle ultrasonic tribometry. A wear model that includes sliding thermal effects as well as thermodynamics consistent with the wear mechanism for DLCs was developed based on empirical results from ultrasonic wear testing to 108 cycles. The model fit both ultrasonic and classic tribometer data for wear of DLCs. Finally, the wear properties of laser hardened steels - SAE 8620, 4140, and 52100 - were studied at high contact pressures and low numbers of cycles. A design of experiments was conducted to understand how the laser processing parameters of power, speed, and beam size, as well as carbon content of the steel, affected surface hardness. A hardness maximum was found at approximately 0.7 wt% carbon most likely resulting from increased amounts of retained austenite. The ratcheting contact fatigue model of Kapoor was found to be useful in predicting the wear results. The empirical model of Clayton and Su and extended by Afferente and Ciavarella, also provided reasonable semi-quantitative contact fatigue life models for these steels.

Fatigue responses of lead zirconate titanate stacks under semibipolar electric cycling with mechanical preload

NASA Astrophysics Data System (ADS)

Wang, Hong; Cooper, Thomas A.; Lin, Hua-Tay; Wereszczak, Andrew A.

2010-10-01

Lead zirconate titanate (PZT) stacks that had an interdigital internal electrode configuration were tested to more than 108 cycles. A 100 Hz semibipolar sine wave with a field range of +4.5/-0.9 kV/mm was used in cycling with a concurrently-applied 20 MPa preload. Significant reductions in piezoelectric and dielectric responses were observed during the cycling depending on the measuring condition. Extensive partial discharges were also observed. These surface events resulted in the erosion of external electrode and the exposure of internal electrodes. Sections prepared by sequential polishing technique revealed a variety of damage mechanisms including delaminations, pores, and etch grooves. The scale of damage was correlated with the degree of fatigue-induced reduction in piezoelectric and dielectric responses. The results from this study demonstrate the feasibility of using a semibipolar mode to drive a PZT stack under a mechanical preload and illustrate the potential fatigue and damages of the stack in service.

Effect of residual stresses induced by prestressing on rolling element fatigue life

NASA Technical Reports Server (NTRS)

Parker, R. J.; Zaretsky, E. V.

1972-01-01

A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.

Influence of Secondary Cyclic Hardening on the Low Cycle Fatigue Behavior of Nitrogen Alloyed 316LN Stainless Steel

NASA Astrophysics Data System (ADS)

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

2013-12-01

In this article, the occurrence of secondary cyclic hardening (SCH) and its effect on high-temperature cyclic deformation and fatigue life of 316LN Stainless steel are presented. SCH is found to result from planar slip mode of deformation and enhance the degree of hardening over and above that resulted from dynamic strain aging. The occurrence of SCH is strongly governed by the applied strain amplitude, test temperature, and the nitrogen content in the 316LN SS. Under certain test conditions, SCH is noticed to decrease the low cycle fatigue life with the increasing nitrogen content.

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

NASA Technical Reports Server (NTRS)

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

2011-01-01

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

Thermal fatigue performance of integrally cast automotive turbine wheels

NASA Technical Reports Server (NTRS)

Humphreys, V. E.; Hofer, K. E.

1980-01-01

Fluidized bed thermal fatigue testing was conducted on 16 integrally cast automotive turbine wheels for 1000-10,000 (600 sec total) thermal cycles at 935/50 C. The 16 wheels consisted of 14 IN-792 + 1% Hf and 2 gatorized AF2-1DA wheels; 6 of the IN-792 + Hf wheels contained crack arrest pockets inside the blade root flange. Temperature transients during the thermal cycling were measured in three calibration tests using either 18 or 30 thermocouples per wheel. Thermal cracking based on crack length versus accumulated cycles was greatest for unpocketed wheels developing cracks in 8-13 cycles compared to 75-250 cycles for unpocketed wheels. However, pocketed wheels survived up to 10,000 cycles with crack lengths less than 20 mm, whereas two unpocketed wheels developed 45 mm long cracks in 1000-2000 cycles.

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

PubMed

Deng, Hailong; Li, Wei; Sakai, Tatsuo; Sun, Zhenduo

2015-12-02

The unexpected failures of structural materials in very high cycle fatigue (VHCF) regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = -1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show that the Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 10⁸ cycles is around 485 MPa. The inclusion-fine granular area (FGA)-fisheye induced failure becomes the main failure mechanism in the VHCF regime, and the local stress around the inclusion play a key role. By using the finite element analysis of representative volume element, the local stress tends to increase with the increase of elastic modulus difference between inclusion and matrix. The predicted crack initiation life occupies the majority of total fatigue life, while the predicted crack growth life is only accounts for a tiny fraction. In view of the good agreement between the predicted and experimental results, the proposed VHCF life prediction model involving crack initiation and growth can be acceptable for inclusion-FGA-fisheye induced failure.

Fatigue resistance of engine-driven rotary nickel-titanium instruments produced by new manufacturing methods.

PubMed

Gambarini, Gianluca; Grande, Nicola Maria; Plotino, Gianluca; Somma, Francesco; Garala, Manish; De Luca, Massimo; Testarelli, Luca

2008-08-01

The aim of the present study was to investigate whether cyclic fatigue resistance is increased for nickel-titanium instruments manufactured by using new processes. This was evaluated by comparing instruments produced by using the twisted method (TF; SybronEndo, Orange, CA) and those using the M-wire alloy (GTX; Dentsply Tulsa-Dental Specialties, Tulsa, OK) with instruments produced by a traditional NiTi grinding process (K3, SybronEndo). Tests were performed with a specific cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals. Results indicated that size 06-25 TF instruments showed a significant increase (p < 0.05) in the mean number of cycles to failure when compared with size 06-25 K3 files. Size 06-20 K3 instruments showed no significant increase (p > 0.05) in the mean number of cycles to failure when compared with size 06-20 GT series X instruments. The new manufacturing process produced nickel-titanium rotary files (TF) significantly more resistant to fatigue than instruments produced with the traditional NiTi grinding process. Instruments produced with M-wire (GTX) were not found to be more resistant to fatigue than instruments produced with the traditional NiTi grinding process.

Life prediction of l6 steel using strain-life curve and cyclic stress-strain curve by means of low cycle fatigue testing

NASA Astrophysics Data System (ADS)

Inamdar, Sanket; Ukhande, Manoj; Date, Prashant; Lomate, Dattaprasad; Takale, Shyam; Singh, RKP

2017-05-01

L6 Steel is used as die material in closed die hot forging process. This material is having some unique properties. These properties are due to its composition. Strain softening is the noticeable property of this material. Due to this in spite of cracking at high stress this material gets plastically deformed and encounters loss in time as well as money. Studies of these properties are necessary to nurture this material at fullest extent. In this paper, numerous experiments have been carried on L6 material to evaluate cyclic Stress - strain behavior as swell as strain-life behavior of the material. Low cycle fatigue test is carried out on MTS fatigue test machine at fully reverse loading condition R=-1. Also strain softening effect on forging metal forming process is explained in detail. The failed samples during low cycle fatigue test further investigated metallurgically on scanning electron microscopy. Based on this study, life estimation of hot forging die is carried out and it’s correlation with actual shop floor data is found out. This work also concludes about effect of pre-treatments like nitro-carburizing and surface coating on L6 steel material, to enhance its fatigue life to certain extent.

Preliminary Study on Fatigue Strengths of Fretted Ti-48Al-2Cr-2Nb

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Lerch, Bradley A.; Draper, Susan L.

2002-01-01

The fatigue behavior (stress-life curve) of gamma titanium aluminide (Ti-48Al-2Cr-2Nb, atomic percent) was examined by conducting two tests: first, a fretting wear test with a fatigue specimen in contact with a typical nickel-based superalloy contact pad in air at temperatures of 296 and 823 K and second, a high-cycle fatigue test of the prefretted Ti-48Al-2Cr-2Nb fatigue specimen at 923 K. Reference high-cycle fatigue tests were also conducted with unfretted Ti-48Al-2Cr-2Nb specimens at 923 K. All Ti-48Al-2Cr-2Nb fatigue specimens were machined from cast slabs. The results indicate that the stress-life results for the fretted Ti-48Al-2Cr-2Nb specimens exhibited a behavior similar to those of the unfretted Ti-48Al-2Cr-2Nb specimens. The values of maximum stress and life for the fretted specimens were almost the same as those for the unfretted specimens. The resultant stress-life curve for the unfretted fatigue specimens was very flat. The flat appearance in the stress-life curve of the unfretted specimens is attributed to the presence of a high density of casting pores. The fatigue strengths of both the fretted and unfretted specimens can be significantly affected by the presence of this porosity, which can decrease the fatigue life of Ti-48Al-2Cr-2Nb. The presence of the porosity made discerning the effect of fretting damage on fatigue strength and life of the specimens difficult.

Oxidation- and Creep-Enhanced Fatigue of Haynes 188 Alloy-Oxide Scale System Under Simulated Pulse Detonation Engine Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.

2002-01-01

The development of the pulse detonation engine (PDE) requires robust design of the engine components that are capable of enduring harsh detonation environments. In this study, a high cycle thermal fatigue test rig was developed for evaluating candidate PDE combustor materials using a CO2 laser. The high cycle thermal fatigue behavior of Haynes 188 alloy was investigated under an enhanced pulsed laser test condition of 30 Hz cycle frequency (33 ms pulse period, and 10 ms pulse width including 0.2 ms pulse spike). The temperature swings generated by the laser pulses near the specimen surface were characterized by using one-dimensional finite difference modeling combined with experimental measurements. The temperature swings resulted in significant thermal cyclic stresses in the oxide scale/alloy system, and induced extensive surface cracking. Striations of various sizes were observed at the cracked surfaces and oxide/alloy interfaces under the cyclic stresses. The test results indicated that oxidation and creep-enhanced fatigue at the oxide scale/alloy interface was an important mechanism for the surface crack initiation and propagation under the simulated PDE condition.

Effect of Stress-Strain Behavior on Low-Cycle Fatigue of Alpha-Beta Titanium Alloys.

DTIC Science & Technology

1980-11-21

and strain excursion, such a curve would appear to fit much of the high temperature hold-time data compiled by Krempl and Wundt [21]. Thus, it might...34Mechanische Relaxation von Kupfer-Einkristallen," Phys. Stat. Sol. 3, 111-120. 21. Krempl, E. and Wundt , B. M., (1971), Hold-Time Effects in High- Temperature Low-Cycle Fatigue, ASTM STP 489. 26 Low

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

NASA Astrophysics Data System (ADS)

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

2015-02-01

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

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

PubMed Central

Lu, Zhe; Myoung, Sang-Won; Jung, Yeon-Gil; Balakrishnan, Govindasamy; Lee, Jeongseung; Paik, Ungyu

2013-01-01

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. PMID:28811441

Isothermal Damage and Fatigue Behavior of SCS-6/Timetal 21S [0/90](Sub S) Composite at 650 Deg C

NASA Technical Reports Server (NTRS)

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.

Probability of failure prediction for step-stress fatigue under sine or random stress

NASA Technical Reports Server (NTRS)

Lambert, R. G.

1979-01-01

A previously proposed cumulative fatigue damage law is extended to predict the probability of failure or fatigue life for structural materials with S-N fatigue curves represented as a scatterband of failure points. The proposed law applies to structures subjected to sinusoidal or random stresses and includes the effect of initial crack (i.e., flaw) sizes. The corrected cycle ratio damage function is shown to have physical significance.

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

PubMed

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.

Low cycle fatigue of PM/HIP astroloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choe, S.J.; Stoloff, N.S.; Duquette, D.J.

Low cycle fatigue and creep-fatigue-environment interactions of PM/HIP Astrology were studied at 650 C and 725 C. Total strain range was varied from 1.5% to 2.7% at a frequency of 0.3Hz. Creep-fatigue tests were performed with 2 min. or 5 min. tensile hold times. All tests were run in high purity argon in an attempt to minimize environmental effects. Employing a tensile hold was more damaging than raising temperature by 75 C. Slopes of Coffin-Manson plots were nearly independent of temperature and hold time. Raising temperature from 650 C to 725 C did not change the transgranular (TG) crack propagationmore » mode, whereas employing hold times caused TG+IG propagation. All samples displayed multiple fracture origins associated with inclusions located at the specimen surface; pre-existing pores did not affect fatigue crack initiation. Examination of secondary cracks showed no apparent creep damage. Oxidation in high purity argon appeared to be the major factor in LCF life degradation due to hold times.« less

Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Hodge, A. J.; Jackson, J. R.

2010-01-01

The issue of fatigue loading of structures composed of composite materials is considered in a requirements document that is currently in place for manned launch vehicles. By taking into account the short life of these parts, coupled with design considerations, it is demonstrated that the necessary coupon level fatigue data collapse to a static case. Data from a literature review of past studies that examined compressive fatigue loading after impact and data generated from this experimental study are presented to support this finding. Damage growth, in the form of infrared thermography, was difficult to detect due to rapid degradation of compressive properties once damage growth initiated. Unrealistically high fatigue amplitudes were needed to fail 5 of 15 specimens before 10,000 cycles were reached. Since a typical vehicle structure, such as the Ares I interstage, only experiences a few cycles near limit load, it is concluded that static compression after impact (CAI) strength data will suffice for most launch vehicle structures.

Effect of grain orientation and coating on thermal fatigue resistance of a directionally solidified superalloy (MAR-M 247)

NASA Technical Reports Server (NTRS)

Bizon, P. T.; Dreshfield, R. L.; Calfo, F. D.

1979-01-01

The effect of off-axis directionally solidified (DS) grain growth on thermal fatigue life of Mar-M 247 alloy was evaluated. Uncoated conventionally cast as well as DS wedge bars were cycled in a burner rig between 1070 C and room temperature. The longitudinal axis and leading edge of the specimen coincided. As the angle between the specimen longitudinal axis and growth axis increased, the thermal fatigue life decreased for both the uncoated and aluminide-coated bars. Life increases of about 50 cycles for the DS conditions were attributed to coating. The decrease in thermal fatigue life with increasing angle is primarily attributed to the increase in modulus of elasticity with increasing angle and not to the intersection of DS grain boundaries with the specimen leading edge. The thermal fatigue cracks were observed to be transgranular in the DS material. Limited tensile and stress-rupture properties of conventionally cast and off-axis DS Mar-M 247 alloy are also presented.

Effect of helium to dpa ratio on fatigue behavior of austenitic stainless steel irradiated to 2 dpa

NASA Astrophysics Data System (ADS)

Ioka, I.; Yonekawa, M.; Miwa, Y.; Mimura, H.; Tsuji, H.; Hoshiya, T.

2000-12-01

The effect of helium due to nuclear transmutation reactions during neutron irradiation on low cycle fatigue life of type 304 stainless steel was investigated. The specimens were irradiated in spectrally tailored capsules in the Japan Materials Testing Reactor (JMTR) at a temperature of 823 K to a neutron fluence of approximately 1×1025 n/m2 (E>1 MeV) and helium levels of 0.8, 2.5 and 8.1 appm. The low cycle fatigue tests were performed in total axial strain ranges of 0.8-1.6% at 823 K. A laser extensometer was used for controlling the axial strain of a specimen under cyclic testing. The difference between unirradiated and irradiated specimens is quite clear and appears to be a reduction by a factor of 2-5 in fatigue life. The helium concentration of the specimen is not the main factor to shorten fatigue life in the present experimental condition.

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

NASA Astrophysics Data System (ADS)

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.

Stiffness reductions during tensile fatigue testing of graphite/epoxy angle-ply laminates

NASA Technical Reports Server (NTRS)

Odom, E. M.; Adams, D. F.

1982-01-01

Tensile fatigue data was generated under carefully controlled test conditions. A computerized data acquisition system was used to permit the measurement of dynamic modulus without interrupting the fatigue cycling. Two different 8-ply laminate configurations, viz, + or - 45 (2s) and + or - 67.5 (2s), of a T300/5208 graphite/epoxy composite were tested. The + or - 45 (2s) laminate did exhibit some modulus decay, although there was no well-defined correlation with applied stress level or number of cycles. The + or - 67.5 (2s) laminate did not exhibit any measurable modulus decay. Secondary effects observed included a small but distinct difference between modulus as measured statically and dynamically, a slight recovery of the modulus decay after a test interruption, and a significant viscoelastic (creep) response of the + or - 45 (2s) laminate during fatigue testing.

Fatigue mechanism verified using photovoltaic properties of Pb(Zr0.52Ti0.48)O3 thin films

NASA Astrophysics Data System (ADS)

Wu, Ming; Li, Wei; Li, Junning; Wang, Shaolan; Li, Yaqi; Peng, Biaolin; Huang, Haitao; Lou, Xiaojie

2017-03-01

The photovoltaic effect and its evolution during electrical fatigue in Pb(Zr0.52Ti0.48)O3 (PZT) thin films have been investigated. It is found that the photovoltaic effect of the as-grown PZT thin film is highly affected by the asymmetric Schottky barriers, which can be tuned by applying an external electric field. During fatigue processes, both open-circuit voltage (Voc) and short-circuit current (Jsc) decrease considerably with the increase of the number of electrical cycles. This phenomenon could be ascribed to the degradation of the interfacial layer between the thin film and the electrode induced by highly energetic charge carriers injected from the electrode during bipolar cycling. Our work sheds light on the physical mechanism of both ferroelectric photovoltaics and polarization fatigue in thin-film ferroelectrics.

Fatigue properties of die cast zinc alloys for automotive lock applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schrems, Karol K.; Dogan, Omer N.; Goodwin, F.E.

2004-06-01

During the 1970’s many automotive lock systems were converted from zinc die casting alloys to engineering plastics for reasons of weight and cost. Recent increases in requirements for precision and security have caused automotive and other lock designers to reconsider zinc alloy die-castings for these applications. To enable this, there is a need for mechanical property data comparable to that of the plastics materials used in these applications. In this work, rotary bending fatigue tests were performed on Alloys 3, 5, ZA-8 and AcuZinc 5 using an R.R. Moore fatigue machine. Testing was performed at 30 Hz and was stoppedmore » at 1x107 cycles. The fatigue limit results were compared to data reported in the literature for higher number of cycles and faster rotations.« less

Modelling of a Francis Turbine Runner Fatigue Failure Process Caused by Fluid-Structure Interaction

NASA Astrophysics Data System (ADS)

Lyutov, A.; Kryukov, A.; Cherny, S.; Chirkov, D.; Salienko, A.; Skorospelov, V.; Turuk, P.

2016-11-01

In the present paper considered is the problem of the numerical simulation of Francis turbine runner fatigue failure caused by fluid-structure interaction. The unsteady 3D flow is modeled simultaneously in the spiral chamber, each wicket gate and runner channels and in the draft tube using the Euler equations. Based on the unsteady runner loadings at each time step stresses in the whole runner are calculated using the elastic equilibrium equations solved with boundary element method. Set of static stress-strain states provides quasi-dynamics of runner cyclic loading. It is assumed that equivalent stresses in the runner are below the critical value after which irreversible plastic processes happen in the runner material. Therefore runner is subjected to the fatigue damage caused by high-cycle fatigue, in which the loads are generally low compared with the limit stress of the material. As a consequence, the stress state around the crack front can be fully characterized by linear elastic fracture mechanics. The place of runner cracking is determined as a point with maximal amplitude of stress oscillations. Stress pulsations amplitude is used to estimate the number of cycles until the moment of fatigue failure, number of loading cycles and oscillation frequency are used to calculate runner service time. Example of the real Francis runner which has encountered premature fatigue failure as a result of incorrect durability estimation is used to verify the developed numerical model.

The development and reliability of a repeated anaerobic cycling test in female ice hockey players.

PubMed

Wilson, Kier; Snydmiller, Gary; Game, Alex; Quinney, Art; Bell, Gordon

2010-02-01

The purpose of this study was to develop and assess the reliability of a repeated anaerobic power cycling test designed to mimic the repeated sprinting nature of the sport of ice hockey. Nineteen female varsity ice hockey players (mean X +/- SD age, height and body mass = 21 +/- 2 yr, 166.6 +/- 6.3 cm and 62.3 +/- 7.3) completed 3 trials of a repeated anaerobic power test on a Monark cycle ergometer on different days. The test consisted of "all-out" cycling for 5 seconds separated by 10 seconds of low-intensity cycling, repeated 4 times. The relative load factor used for the resistance setting was equal to 0.095 kg per kilogram body mass. There was no significant difference between the peak 5-second power output (PO), mean PO, or the fatigue index (%) among the 3 different trials. The peak 5-second PO was 702.6 +/- 114.8 w and 11.3 +/- 1.1 w x kg, whereas the mean PO across the 4 repeats was 647.1 +/- 96.3 w and 10.4 +/- 1.0 w x kg averaged for the 3 different tests. The fatigue index averaged 17.8 +/- 6.5%. The intraclass correlation coefficient for peak 5-second, mean PO, and fatigue index was 0.82, 0.86, and 0.82, respectively. This study reports the methodology of a repeated anaerobic power cycling test that was reliable for the measurement of PO and calculated fatigue index in varsity women ice hockey players and can be used as a laboratory-based assessment of repeated anaerobic fitness.

Corrosion fatigue in nitrocarburized quenched and tempered steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karim Khani, M.; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-{mu}m-thick electroless Ni-P layer, in order to compare corrosion fatigue behaviormore » between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 10{sup 8} cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skochko, G.W.; Herrmann, T.P.

Axial load cycling fatigue tests of threaded fasteners are useful in determining fastener fatigue failure or design properties. By using appropriate design factors between the failure and design fatigue strengths, such tests are used to establish fatigue failure and design parameters of fasteners for axial and bending cyclic load conditions. This paper reviews the factors which influence the fatigue strength of low Alloy steel threaded fasteners, identifies those most significant to fatigue strength, and provides design guidelines based on the direct evaluation of fatigue tests of threaded fasteners. Influences on fatigue strength of thread manufacturing process (machining and rolling ofmore » threads), effect of fastener membrane and bending stresses, thread root radii, fastener sizes, fastener tensile strength, stress relaxation, mean stress, and test temperature are discussed.« less

Fracture mechanics and corrosion fatigue.

NASA Technical Reports Server (NTRS)

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

1972-01-01

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

The Effect of a Standardized Ginger Extract on Chemotherapy-Induced Nausea-Related Quality of Life in Patients Undergoing Moderately or Highly Emetogenic Chemotherapy: A Double Blind, Randomized, Placebo Controlled Trial.

PubMed

Marx, Wolfgang; McCarthy, Alexandra L; Ried, Karin; McKavanagh, Dan; Vitetta, Luis; Sali, Avni; Lohning, Anna; Isenring, Elisabeth

2017-08-12

Ginger supplementation could be an effective adjuvant treatment for chemotherapy-induced nausea (CIN). The aim of this clinical trial was to address significant methodological limitations in previous trials. Patients (N = 51) were randomly allocated to receive either 1.2 g of standardised ginger extract or placebo per day, in addition to standard anti-emetic therapy, during the first three cycles of chemotherapy. The primary outcome was CIN-related quality of life (QoL) measured with the Functional Living Index- Emesis (FLIE) questionnaire. Secondary outcomes included acute and delayed nausea, vomiting, and retching as well as cancer-related fatigue, nutritional status, and CIN and vomiting-specific prognostic factors. Over three consecutive chemotherapy cycles, nausea was more prevalent than vomiting (47% vs. 12%). In chemotherapy Cycle 1, intervention participants reported significantly better QoL related to CIN ( p = 0.029), chemotherapy-induced nausea and vomiting (CINV)-related QoL ( p = 0.043), global QoL ( p = 0.015) and less fatigue ( p = 0.006) than placebo participants. There were no significant results in Cycle 2. In Cycle 3, global QoL ( p = 0.040) and fatigue ( p = 0.013) were significantly better in the intervention group compared to placebo. This trial suggests adjuvant ginger supplementation is associated with better chemotherapy-induced nausea-related quality of life and less cancer-related fatigue, with no difference in adverse effects compared to placebo.

Fatigue Crack Growth Properties of Rail Steels

DOT National Transportation Integrated Search

1981-10-01

Fatigue crack propagation properties of rail steels were determined experimentally. The investigation covered 66 rail steels. The effects of the following parameters were studied: stress ratio (ratio of minimum to maximum stress in a cycle), frequenc...

Effect of Grinding and Multi-Stimuli Aging on the Fatigue Strength of a Y-TZP Ceramic.

PubMed

Silvestri, Tais; Pereira, Gabriel Kalil Rocha; Guilardi, Luis Felipe; Rippe, Marilia Pivetta; Valandro, Luiz Felipe

2018-01-01

This study aimed to investigate the effect of grinding and multi-stimuli aging on the fatigue strength, surface topography and the phase transformation of Y-TZP ceramic. Discs were manufactured according to ISO-6872:2008 for biaxial flexure testing (diameter: 15 mm; thickness: 1.2 mm) and randomly assigned considering two factors "grinding" and "aging": C- control (as-sintered); CA- control + aging; G- ground; GA- ground + aging. Grinding was carried out with coarse diamond burs under water-cooling. Aging protocols consisted of: autoclave (134°C, 2 bars pressure, 20 hours), followed by storage for 365 days (samples were kept untouched at room temperature), and by mechanical cycling (106 cycles by 20 Hz under a load of 50% from the biaxial flexure monotonic tests). Flexural fatigue strengths (20,000 cycles; 6 Hz) were determined under sinusoidal cyclic loading using staircase approach. Additionally, surface topography analysis by FE-SEM and phase transformation analysis by X-ray Diffractometry were performed. Dixon and Mood methodology was used to analyze the fatigue strength data. Grinding promotes alterations of topographical pattern, while aging apparently did not alter it. Grinding triggered t-m phase transformation without impacting the fatigue strength of the Y-TZP ceramic; and aging promoted an intense t-m transformation that resulted in a toughening mechanism leading to higher fatigue strength for as-sintered condition, and a tendency of increase for ground condition (C < CA; G = GA). It concludes that grinding and aging procedures did not affect deleteriously the fatigue strength of the evaluated Y-TZP ceramic, although, it promotes surface topography alterations, except to aging, and t-m phase transformation.

The effects of autoclave sterilization on the cyclic fatigue resistance of ProTaper Universal, ProTaper Next, and ProTaper Gold nickel-titanium instruments

PubMed Central

2017-01-01

Objectives It was aimed to compare the cyclic fatigue resistances of ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG) and the effects of sterilization by autoclave on the cyclic fatigue life of nickel-titanium (NiTi) instruments. Materials and Methods Eighty PTU, 80 PTN, and 80 PTG were included to the present study. Files were tested in a simulated canal. Each brand of the NiTi files were divided into 4 subgroups: group 1, as received condition; group 2, pre-sterilized instruments exposed to 10 times sterilization by autoclave; group 3, instruments tested were sterilized after being exposed to 25%, 50%, and 75% of the mean cycles to failure, then cycled fatigue test was performed; group 4, instruments exposed to the same experiment with group 3 without sterilization. The number of cycles to failure (NCF) was calculated. The data was statistically analyzed by using one-way analysis of variance and post hoc Tukey tests. Results PTG showed significantly higher NCF than PTU and PTN in group 1 (p < 0.05). Sterilization significantly increased the NCF of PTN and PTG (p < 0.05) in group 2. PTN in group 3 had significantly higher cyclic fatigue resistance than PTN group 4 (p < 0.05). Also, significantly higher NCF was observed for PTG in group 2 than in groups 3 and 4 (p < 0.05). Conclusions PTG instrument made of new gold alloy was more resistant to fatigue failure than PTN and PTU. Autoclaving increased the cyclic fatigue resistances of PTN and PTG. PMID:29142878

Protection of muscle membrane excitability during prolonged cycle exercise with glucose supplementation.

PubMed

Stewart, R D; Duhamel, T A; Foley, K P; Ouyang, J; Smith, I C; Green, H J

2007-07-01

To determine if exercise-induced depressions in neuromuscular function are altered with oral glucose supplementation, 15 untrained participants (Vo2 peak = 45 +/- 2 ml x kg(-1) x min(-1), mean +/- SE) performed prolonged cycle exercise at approximately 60% Vo2 peak on two occasions: without glucose supplementation (NG) and with oral glucose supplementation (G). The oral G began at 30 min of exercise and was administered every 15 min (total ingested = 1.23 +/- 0.11 g carbohydrate/kg body mass). Quadriceps isometric properties and membrane excitability were assessed prior to exercise, after 90 min of exercise, and at fatigue. Cycle time to fatigue was greater (P < 0.05) in G compared with NG (137 +/- 7 vs. 115 +/- 6 min). Progressive reductions (P < 0.05) in maximal voluntary contraction (MVC, N) were observed for NG at 90 min (441 +/- 29) and at fatigue (344 +/- 33) compared with pre-exercise (666 +/- 30). At fatigue in G, the reduction in MVC was not as pronounced (P < 0.05) as in NG. Motor unit activation assessed with the interpolated twitch technique during an MVC following exercise was not different between conditions. During cycling, the G condition also resulted in a higher (P < 0.05) muscle compound potential (M-wave) amplitude (mV) at both 90 min (+50%) and at fatigue (+87%) compared with NG. Similar effects were also found M-wave area (mV/ms). These results suggest that the ergogenic effect of glucose supplementation occurs not as a result of decreased neural activation but to improved muscle function, possibly as a consequence of protection of muscle membrane excitability.

Fatigue strength of socket welded pipe joint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higuchi, Makoto; Hayashi, Makoto; Yamauchi, Takayoshi

1995-12-01

Fully reversed four point bending fatigue tests were carried out on small diameter socket welded joints made of carbon steels. Experimental parameters were pipe diameter, thicknesses of pipe and socket wall, throat depth and shape of fillet welds, slip-on and diametral gaps in the socket welding, lack of penetration at the root of fillet welds, and peening of fillet welds. In most cases a fatigue crack started from the root of the fillet, but in the case of higher stress amplitude, it tended to start from the toe of fillet. The standard socket welded joint for a pipe with amore » 50 mm nominal diameter showed a relatively low fatigue strength of 46 MPa in stress amplitude at the 10{sup 7} cycles failure life. This value corresponds to about 1/5 of that for the smoothed base metal specimens in axial fatigue. The fatigue strength decreased with increasing pipe diameter, and increased with increasing thickness of the pipe and socket wall. The effects of throat depth and shape of fillet welds on fatigue strength were not significant. Contrary to expectation, the fatigue strength of a socket welded joint without slip-on gap is Higher than that of the joint with a normal gap. A lack of penetration at the root deleteriously reduced fatigue strength, showing 14 MPa in stress amplitude at the 10{sup 7} cycles failure life for the 50 mm diameter socket joint.« less

Thermo-elastic nondestructive evaluation of fatigue damage in PMR-15 resin

NASA Astrophysics Data System (ADS)

Welter, J. T.; Sathish, S.; Tandon, G. P.; Schehl, N.; Cherry, M.; Nalladega, V.; Lindgren, E. A.; Hall, R.

2012-05-01

Thermoset polyimide resins are used as the polymer matrix in high temperature composites for aerospace applications such as engine shrouds. At these locations the components have to withstand high temperatures and significant vibration. A number of studies have investigated the effects of thermal exposure on mechanical properties of polyimide resins, and the effects of fatigue on thermoplastics have been discussed at length. However, the effects of fatigue on thermosets, in particular polyimides, have largely been overlooked. In this paper we present studies of nondestructive evaluation of fatigue damage in a thermoset polyimide resin, PMR-15, performed by measuring the changes in the evolution of heat in the samples during cyclic loading. The temperature changes are measured using a high sensitivity IR camera as a function of number of fatigue cycles. Interrupted fatigue tests were performed on four samples. The temperature rise during an increment of fatigue cycling shows two linear regions each with a different slope (region 1 and region 2). Region 1 remains constant for every increment of fatigue, while region 2 increases. The onset of region 2 occurs at the same increase in temperature due to hysteretic heating for all samples. Experimental observations are explained using a phenomenological two phase model based on crosslinking density variations in observed in other thermoset resins at microscopic scales. The results of these experiments are discussed in reference to utilizing this technique for detection and evaluation of fatigue in PMR-15 resin and composites.

Highly Damping Hard Coatings for Protection of Titanium Blades

DTIC Science & Technology

2005-10-01

Cycle Fatigue in Gas Turbine Engines for Land, Sea and Air Vehicles (pp. 11-1 – 11-16). Meeting Proceedings RTO-MP-AVT-121, Paper 11. Neuilly-sur...121. Evaluation, Control and Prevention of High Cycle Fatigue in Gas Turbine Engines for Land, Sea and Air Vehicles., The original document contains...result of microplastic deformation of the coating in the nano-structured state, is controlled at alternating loading by reversible phenomena of vacancy

Properties of materials in high pressure hydrogen at cryogenic, room, and elevated temperatures

NASA Technical Reports Server (NTRS)

Harris, J. A., Jr.; Vanwanderham, M. C.

1973-01-01

Various tests were conducted to determine the mechanical properties of 12 alloys that are commonly used or proposed for use in pressurized gaseous hydrogen or hydrogen containing environments. Properties determined in the hydrogen environments were compared to properties determined in a pure helium environment at the same conditions to establish environmental degradation. The specific mechanical properties tested include: high-cycle fatigue, low-cycle fatigue, fracture mechanics, creep-rupture, and tensile.

Strainrange partitioning life predictions of the long time metal properties council creep-fatigue tests

NASA Technical Reports Server (NTRS)

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

1979-01-01

The method of strainrange partitioning is used to predict the cyclic lives of the Metal Properties Council's long time creep-fatigue interspersion tests of several steel alloys. Comparisons are made with predictions based upon the time- and cycle-fraction approach. The method of strainrange partitioning is shown to give consistently more accurate predictions of cyclic life than is given by the time- and cycle-fraction approach.

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

NASA Technical Reports Server (NTRS)

Kihm, Frederic; Rizzi, Stephen A.

2014-01-01

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

Thermal fatigue life evaluation of SnAgCu solder joints in a multi-chip power module

NASA Astrophysics Data System (ADS)

Barbagallo, C.; Malgioglio, G. L.; Petrone, G.; Cammarata, G.

2017-05-01

For power devices, the reliability of thermal fatigue induced by thermal cycling has been prioritized as an important concern. The main target of this work is to apply a numerical procedure to assess the fatigue life for lead-free solder joints, that represent, in general, the weakest part of the electronic modules. Starting from a real multi-chip power module, FE-based models were built-up by considering different conditions in model implementation in order to simulate, from one hand, the worst working condition for the module and, from another one, the module standing into a climatic test room performing thermal cycles. Simulations were carried-out both in steady and transient conditions in order to estimate the module thermal maps, the stress-strain distributions, the effective plastic strain distributions and finally to assess the number of cycles to failure of the constitutive solder layers.

Fatigue and damage tolerance scatter models

NASA Astrophysics Data System (ADS)

Raikher, Veniamin L.

1994-09-01

Effective Total Fatigue Life and Crack Growth Scatter Models are proposed. The first of them is based on the power form of the Wohler curve, fatigue scatter dependence on mean life value, cycle stress ratio influence on fatigue scatter, and validated description of the mean stress influence on the mean fatigue life. The second uses in addition are fracture mechanics approach, assumption of initial damage existence, and Paris equation. Simple formulas are derived for configurations of models. A preliminary identification of the parameters of the models is fulfilled on the basis of experimental data. Some new and important results for fatigue and crack growth scatter characteristics are obtained.

Effect of ultraviolet light on fatigue of lead zirconate titanate thin-film capacitors

NASA Astrophysics Data System (ADS)

Lee, J.; Esayan, S.; Safari, A.; Ramesh, R.

1994-07-01

Fatigue of Pb(Zr0.52Ti0.48)O3 (PZT) thin-film capacitors was studied under UV light (He-Cd laser, λ=325 nm). The remanent polarization of the PZT film capacitors increased upon light illumination. Fatigue resistance was also improved under UV light. During fatigue test, the change in polarization of PZT films upon UV light illumination increased gradually with cycling. These results were examined within the framework of the polarization screening model, which is suggested as an essential process for fatigue. This leads to a conclusion that more charged defects are involved in the fatigue process through internal screening of polarization.

Low cycle fatigue properties of MAR-M-246 Hf in hydrogen. [a cast nickel-base alloy

NASA Technical Reports Server (NTRS)

Warren, J. R.

1979-01-01

The transverse, low cycle fatigue properties were determined for directionally solidified and single crystal samples of a cast nickel-base alloy proposed for use in space propulsion systems in pure or partial high pressure hydrogen environments at elevated temperatures. The test temperature was 760 C (1400F) and the pressure of the gaseous hydrogen was 34.5 MPa (5000 psig). Low cycle fatique life was established by strain controlled testing using smooth specimens and a servohydraulic closed-loop test machine modified with a high pressure environmental chamber. Results and conclusions are discussed.

A Cyclic-Plasticity-Based Mechanistic Approach for Fatigue Evaluation of 316 Stainless Steel Under Arbitrary Loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barua, Bipul; Mohanty, Subhasish; Listwan, Joseph T.

In this paper, a cyclic-plasticity based fully mechanistic fatigue modeling approach is presented. This is based on time-dependent stress-strain evolution of the material over the entire fatigue life rather than just based on the end of live information typically used for empirical S~N curve based fatigue evaluation approaches. Previously we presented constant amplitude fatigue test based related material models for 316 SS base, 508 LAS base and 316 SS- 316 SS weld which are used in nuclear reactor components such as pressure vessels, nozzles, and surge line pipes. However, we found that constant amplitude fatigue data based models have limitationmore » in capturing the stress-strain evolution under arbitrary fatigue loading. To address the above mentioned limitation, in this paper, we present a more advanced approach that can be used for modeling the cyclic stress-strain evolution and fatigue life not only under constant amplitude but also under any arbitrary (random/variable) fatigue loading. The related material model and analytical model results are presented for 316 SS base metal. Two methodologies (either based on time/cycle or based on accumulated plastic strain energy) to track the material parameters at a given time/cycle are discussed and associated analytical model results are presented. From the material model and analytical cyclic plasticity model results, it is found that the proposed cyclic plasticity model can predict all the important stages of material behavior during the entire fatigue life of the specimens with more than 90% accuracy« less

A Cyclic-Plasticity-Based Mechanistic Approach for Fatigue Evaluation of 316 Stainless Steel Under Arbitrary Loading

DOE PAGES

Barua, Bipul; Mohanty, Subhasish; Listwan, Joseph T.; ...

2017-12-05

In this paper, a cyclic-plasticity based fully mechanistic fatigue modeling approach is presented. This is based on time-dependent stress-strain evolution of the material over the entire fatigue life rather than just based on the end of live information typically used for empirical S~N curve based fatigue evaluation approaches. Previously we presented constant amplitude fatigue test based related material models for 316 SS base, 508 LAS base and 316 SS- 316 SS weld which are used in nuclear reactor components such as pressure vessels, nozzles, and surge line pipes. However, we found that constant amplitude fatigue data based models have limitationmore » in capturing the stress-strain evolution under arbitrary fatigue loading. To address the above mentioned limitation, in this paper, we present a more advanced approach that can be used for modeling the cyclic stress-strain evolution and fatigue life not only under constant amplitude but also under any arbitrary (random/variable) fatigue loading. The related material model and analytical model results are presented for 316 SS base metal. Two methodologies (either based on time/cycle or based on accumulated plastic strain energy) to track the material parameters at a given time/cycle are discussed and associated analytical model results are presented. From the material model and analytical cyclic plasticity model results, it is found that the proposed cyclic plasticity model can predict all the important stages of material behavior during the entire fatigue life of the specimens with more than 90% accuracy« less

Autonomic nervous system function, activity patterns, and sleep after physical or cognitive challenge in people with chronic fatigue syndrome.

PubMed

Cvejic, Erin; Sandler, Carolina X; Keech, Andrew; Barry, Benjamin K; Lloyd, Andrew R; Vollmer-Conna, Uté

2017-12-01

To explore changes in autonomic functioning, sleep, and physical activity during a post-exertional symptom exacerbation induced by physical or cognitive challenge in participants with chronic fatigue syndrome (CFS). Thirty-five participants with CFS reported fatigue levels 24-h before, immediately before, immediately after, and 24-h after the completion of previously characterised physical (stationary cycling) or cognitive (simulated driving) challenges. Participants also provided ratings of their sleep quality and sleep duration for the night before, and after, the challenge. Continuous ambulatory electrocardiography (ECG) and physical activity was recorded from 24-h prior, until 24-h after, the challenge. Heart rate (HR) and HR variability (HRV, as high frequency power in normalized units) was derived from the ECG trace for periods of wake and sleep. Both physical and cognitive challenges induced an immediate exacerbation of the fatigue state (p<0.001), which remained elevated 24-h post-challenge. After completing the challenges, participants spent a greater proportion of wakeful hours lying down (p=0.024), but did not experience significant changes in sleep quality or sleep duration. Although the normal changes in HR and HRV during the transition from wakefulness to sleep were evident, the magnitude of the increase in HRV was significantly lower after completing the challenge (p=0.016). Preliminary evidence of reduced nocturnal parasympathetic activity, and increased periods of inactivity, were found during post-exertional fatigue in a well-defined group of participants with CFS. Larger studies employing challenge paradigms are warranted to further explore the underlying pathophysiological mechanisms of post-exertional fatigue in CFS. Copyright © 2017 Elsevier Inc. All rights reserved.

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

NASA Technical Reports Server (NTRS)

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

2006-01-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kibitkin, Vladimir V., E-mail: vvk@ispms.tsc.ru; Solodushkin, Andrey I., E-mail: s.ai@sibmail.com; Pleshanov, Vasily S., E-mail: vsp@ispms.tsc.ru

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

Real Time Fatigue Damage Growth Assessment of a Composite Three-Stringer Panel Using Passive Thermography

NASA Technical Reports Server (NTRS)

Zalameda, Joseph N.; Burke, Eric R.; Horne, Michael R.; Bly, James B.

2015-01-01

Fatigue testing of advanced composite structures is critical to validate both structural designs and damage prediction models. In-situ inspection methods are necessary to track damage onset and growth as a function of load cycles. Passive thermography is a large area, noncontact inspection technique that is used to detect composite damage onset and growth in real time as a function of fatigue cycles. The thermal images are acquired in synchronicity to the applied compressive load using a dual infrared camera acquisition system for full (front and back) coverage. Image processing algorithms are investigated to increase defect contrast areas. The thermal results are compared to non-immersion ultrasound inspections and acoustic emission data.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a "sandwich structure" as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50-55% of ultimate tensile strength). The dynamic modulus (E(⁎)) was found to stay almost constant at 47GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effect of water temperature on cyclic fatigue properties of glass-fiber-reinforced hybrid composite resin and its fracture pattern after flexural testing.

PubMed

Kuroda, Soichi; Shinya, Akikazu; Vallittu, Pekka K; Nakasone, Yuji; Shinya, Akiyoshi

2013-02-01

To evaluate in vitro the influence of dynamic loading applied to a glass-fiber-reinforced hybrid composite resin on its flexural strength in a moist, simulated oral environment. Three-point flexural strength specimens were subjected to cyclic loading in water at 37°C and 55°C to investigate the influence of immersion temperature on impact fatigue properties. Specimens were subjected to cyclic impact loading at 1 Hz for up to 5 × 105 cycles to obtain the number of cycles to failure, the number of unbroken specimens after 5 × 105 cycles, and the residual flexural strength of unbroken specimens. Maximum loads of 100, 200, and 300 N were chosen for both the non-reinforced and the glass-fiber reinforced hybrid composite resins. The mean residual flexural strength for 100 N impact loading at temperatures of 37°C and 55°C was 634 and 636 MPa, respectively. All specimens fractured at fewer than 5 × 105 cycles for loads of 200 and 300 N. Reduced numbers of cycles to fracture and lower fatigue values were observed as both the maximum load and immersion temperature increased.

High Cycle Fatigue (HCF) Science and Technology Program 2000 Annual Report

DTIC Science & Technology

2000-01-01

in an area of deep compressive stress. • Results of industry and government testing have indicated the ability to stop crack initiation and...fatigue crack nucleation process with the cyclic deformation behavior of the alloy for different microstructures and crystallographic texture ... texture combinations investigated, bimodal fine uni-rolled and lamellar cross-rolled displayed superior fatigue properties to the remaining four

The effect of matrix microstructure on cyclic response and fatigue behavior of particle- reinforced 2219 aluminum: Part I. room temperature behavior

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; van Aken, D. C.

1995-12-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and overaged 2219/TiC/15p and unreinforced 2219 Al were investigated using plastic strain-controlled and stress-controlled testing. In addition, the influence of grain size on the particle-reinforced materials was examined. In both reinforced and unreinforced materials, the naturally aged conditions were cyclically unstable, exhibiting an initial hardening behavior followed by an extended region of cyclic stability and ultimately a softening region. The overaged reinforced material was cyclically stable for the plastic strains examined, while the overaged unreinforced material exhibited cyclic hardening at plastic strains greater than 2.5 × 10-4. Decreasing grain size of particle-reinforced materials modestly increased the cyclic flow stress of both naturally aged and overaged materials. Reinforced and unreinforced materials exhibited similar fatigue life behaviors; however, the reinforced and unreinforced naturally aged materials had superior fatigue lives in comparison to the overaged materials. Grain size had no effect on the fatigue life behavior of the particle-reinforced materials. The fatigue lives were strongly influenced by the presence of clusters of TiC particles and exogenous Al3Ti intermetallics.

Corrosion fatigue of high strength fastener materials in seawater

NASA Technical Reports Server (NTRS)

Tipton, D. G.

1983-01-01

Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

Corrosion fatigue of high strength fastener materials in seawater

NASA Astrophysics Data System (ADS)

Tipton, D. G.

1983-12-01

Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

Assessment of fatigue life of remanufactured impeller based on FEA

NASA Astrophysics Data System (ADS)

Xu, Lei; Cao, Huajun; Liu, Hailong; Zhang, Yubo

2016-09-01

Predicting the fatigue life of remanufactured centrifugal compressor impellers is a critical problem. In this paper, the S-N curve data were obtained by combining experimentation and theory deduction. The load spectrum was compiled by the rain-flow counting method based on the comprehensive consideration of the centrifugal force, residual stress, and aerodynamic loads in the repair region. A fatigue life simulation model was built, and fatigue life was analyzed based on the fatigue cumulative damage rule. Although incapable of providing a high-precision prediction, the simulation results were useful for the analysis of fatigue life impact factors and fatigue fracture areas. Results showed that the load amplitude greatly affected fatigue life, the impeller was protected from running at over-speed, and the predicted fatigue life was satisfied within the next service cycle safely at the rated speed.

Fatigue Crack Initiation Properties of Rail Steels

DOT National Transportation Integrated Search

1982-01-01

Fatigue crack initiation properties of rail-steels were determined experimentally. One new and four used rail steels were investigated. The effects of the following parameters were studied: stress ratio (ratio of minimum to maximum stress in a cycle)...

Fatigue reliability of steel highway bridge details.

DOT National Transportation Integrated Search

2001-08-01

The expected life of a steel highway bridge subjected to random, variable-amplitude traffic cycles is highly dependent on damage accumulation caused by various fatigue mechanisms. This study addressed some of the issues associated with developing pro...

The tensile and fatigue properties of DIN 1.4914 martensitic stainless steel after 590 MeV proton irradiation

NASA Astrophysics Data System (ADS)

Marmy, P.; Victoria, M.

1992-09-01

Tensile and low cycle fatigue subsize specimens of DIN 1.4914 martensitic steel (MANET) have been irradiated with 590 MeV protons to doses up to 1 dpa and at temperatures between 363 and 703 K. The helium produced by spallation reactions was measured as 130 appm/dpa. A strong radiation hardening is found, which decreases as the irradiation temperature increases. The tensile elongation is reduced after irradiation, but the fracture mode is always ductile and transgranular. The radition hardening produced at low irradiation temperatures is recovered after annealing at higher temperatures. Continous softening is observed during low cycle fatigue testing. The rate of softening of the irradiated material is stonger than that of the unirradiated material and tends to reach the saturation level of the latter. The irradiation badly affects the fatigue life, particularly in the temperature domain of dynamic strain ageing between 553 and 653 K.

Electrical fatigue behaviour in lead zirconate titanate: an experimental and theoretical study

NASA Astrophysics Data System (ADS)

Bhattacharyya, Mainak; Arockiarajan, A.

2013-08-01

A systematic investigation on electrical fatigue in lead zirconate titanate (PZT) is carried out for different loading frequencies. Experiments are conducted up to 106 cycles to measure the electrical displacement and longitudinal strain on bulk ceramics in the bipolar mode with large electrical loading conditions. A simplified macroscopic model based on physical mechanisms of domain switching is developed to predict the non-linear behaviour. In this model, the volume fraction of a domain is used as the internal variable by considering the mechanisms of domain nucleation and propagation (domain wall movement). The measured material properties at different fatigue cycles are incorporated into the switching model as damage parameters and the classical strain versus electric field and electric displacement versus electric field curves are simulated. Comparison between the experiments and simulations shows that the proposed model can reproduce the characteristics of non-linear as well as fatigue responses.

Improvement of fatigue resistance for multilayer lead zirconate titanate (PZT)-based ceramic actuators by external mechanical loads

NASA Astrophysics Data System (ADS)

Yang, Gang; Yue, Zhenxing; Ji, Ye; Chu, Xiangcheng; Li, Longtu

2008-12-01

The influence of external compressive loads, applied along a direction perpendicular to polarization, on fatigue behaviors of multilayer lead zirconate titanate (PZT)-based ceramic actuators was investigated. Under no external mechanical load, a normal fatigue behavior was observed, demonstrating that both switching polarization (Pswitching) and remnant polarization (Pr) progressively decreased with increasing switching cycles due to domain pinning by charge point defects. However, an anomalous enhancement in both switching and remnant polarizations was observed upon application of the external compressive loads. After 5×106 cycles of polarization switching, Pswitching and Pr increase by about 13% and 6% at 40 MPa, respectively, while Pswitching and Pr increase by about 11% and 21% at 60 MPa, respectively. The improvement of fatigue resistance can be attributed to non-180° domain switching and suppression of microcracking, triggered by external mechanical loads.