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Artykuły w czasopismach na temat "High fatigue cycles"
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Oshida, Yoshiki, i P. C. Chen. "High and Low-Cycle Fatigue Damage Evaluation of Multilayer Thin Film Structure". Journal of Electronic Packaging 113, nr 1 (1.03.1991): 58–62. http://dx.doi.org/10.1115/1.2905367.
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A five-layered (Cu/Cr/Kapton® /Cr/Cu) metallic thin film structure was subjected to a completely reversed bending fatigue cycling with a wide ranges of applied strain amplitudes from 0.25 percent to about 30 percent. A new model for determination of the number of cycles to fatigue failure NF was proposed for single-crack and multi-crack formations. Within a strain amplitude ranging from 1 to 10 percent, a Manson-Coffin’s relationship was recognized for both the number of cycles to crack initiation NC and NF with exponents of 0.39 and 0.51, respectively. Selected fatigued test samples were further subjected to X-ray diffraction line analysis for dislocation density (ρ) calculation, which was related to the number of fatigue cycles N and strain amplitude (Δ εT) in an empirical formula. It was also found that dislocation densities accumulated up to both Nc and NF were related to applied strain amplitudes. Consequently, if applied strain amplitude is known and progressive change in dislocation density is measured, one can predict the remaining fatigue life as well as fatigue cycles which were already consumed.
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Heinz, Stefan, i Dietmar Eifler. "Very High Cycle Fatigue and Damage Behavior of Ti6Al4V". Key Engineering Materials 664 (wrzesień 2015): 71–80. http://dx.doi.org/10.4028/www.scientific.net/kem.664.71.
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High frequency fatigue tests were carried out with a 20 kHz ultrasonic testing facility to investigate the cyclic deformation behavior of Ti6Al4V in the Very High Cycle Fatigue (VHCF) regime in detail. The S,Nf -curve at the stress ratio R = -1 shows a significant decrease of the 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. Scanning electron microscopy as well as light microscopy were used to investigate the internal crack initiation phenomenon in the VHCF-regime. Beside the primary fatigue crack additional defects like micro cracks and crack clusters were observed in the fatigued specimens. SEM-investigations of specimens which were loaded up to 1010 cycles without failure show irreversible microstructural changes inside the specimens. Two step tests were performed to evaluate the influence of internal fatigue induced defects observed in specimens which did not fail within 1010 cycles.
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Zhang, Wei Chang, Ming Liang Zhu i Fu Zhen Xuan. "Experimental Characterization of Competition of Surface and Internal Damage in Very High Cycle Fatigue Regime". Key Engineering Materials 754 (wrzesień 2017): 79–82. http://dx.doi.org/10.4028/www.scientific.net/kem.754.79.
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Axially push-pull cyclic tests of a low strength rotor steel were performed up to the very high cycle fatigue regime at ambient environment under ultrasonic frequency. Fatigue tests were interrupted at selected number of cycles for surface morphology observation and roughness measurement with the help of a 3D surface measurement system (Alicona InfiniteFocusSL). The fatigue extrusions and slip band developed on the specimen surface were recorded. The influence of stress level on the number and morphology of slip band was discussed. The surface roughness of fatigue specimens was found to be increased with the increasing of fatigue cycles. The fatigued specimens were finally cracked from surface or interior micro-defects after observation of fracture surface by scanning electron microscopy. The internal damage behavior consists of crack initiation and early propagation from micro-defect, crack growth within the fish eye, and fast crack growth. It is observed that there exists a competition between surface and internal fatigue damage in the very high cycle fatigue regime, i.e., surface damage is gradually developed with the increasing of fatigue cycles, while the critical interior micro-defect can be dominant for fatigue cracking.
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Weibel, Dominic, Frank Balle i Daniel Backe. "Ultrasonic Fatigue of CFRP - Experimental Principle, Damage Analysis and Very High Cycle Fatigue Properties". Key Engineering Materials 742 (lipiec 2017): 621–28. http://dx.doi.org/10.4028/www.scientific.net/kem.742.621.
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Structural aircraft components are often subjected to more than 108 loading cycles during their service life. Therefore the increasing use of carbon fiber reinforced polymers (CFRP) as primary lightweight structural materials leads to the demand of a precise knowledge of the fatigue behavior and the corresponding failure mechanisms in the very high cycle fatigue (VHCF) range. To realise fatigue investigations for more than 108 loading cycles in an economic reasonable time a novel ultrasonic fatigue testing facility (UTF) for cyclic three-point bending was developed and patented. To avoid critical internal heating due to viscoelastic damping and internal friction, the fatigue testing at 20 kHz is performed in resonance as well as in pulse-pause control resulting in an effective testing frequency of ~1 kHz and the capability of performing 109 loading cycles in less than twelve days. The fatigue behavior of carbon fiber twill 2/2 fabric reinforced polyphenylene sulfide (CF-PPS) and carbon fiber 4-H satin fabric reinforced epoxy resin (CF-EP) was investigated. To study the induced fatigue damage of CF-PPS and CF-EP in the VHCF regime in detail, the fatigue mechanisms and damage development were characterized by light optical and SEM investigations during interruptions of constant amplitude tests (CAT). Lifetime-oriented investigations showed a significant decrease of the bearable stress amplitudes of CF-PPS and CFEP in the range between 106 to 109 loading cycles. The ultrasonically fatigued thermoset matrix composite showed a significantly different VHCF behavior in comparison to the investigated thermoplastic matrix composite: No fiber-matrix debonding or transversal cracks were present on the specimen edges, but a sudden specimen failure along with carbon fiber breakage have been observed. The fatigue shear strength at 109 cycles for CF-PPS could be determined to τa, 13 = 4.2 MPa and to τa, 13 = 15.8 MPa for the thermoset material CF-EP.
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He, Chao, Yong Jie Liu i Qing Yuan Wang. "Very High Cycle Fatigue Properties of Welded Joints under High Frequency Loading". Advanced Materials Research 647 (styczeń 2013): 817–21. http://dx.doi.org/10.4028/www.scientific.net/amr.647.817.
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Very high cycle fatigue (VHCF) properties of welded joints under ultrasonic fatigue loading have been investigated for titanium alloy (TI-6Al-4V) and bridge steel (Q345). Ultrasonic fatigue tests of base metal and welded joints were carried out in ambient air at room temperature at a stress ratio R=-1. It was observed that the fatigue strength of welded joints reduced by 50-60% as compared to the base metal. The S-N fatigue curves in the range of 107~109 cycles of base metal and welded joints for both materials exhibited the characteristic of continually decreasing type. The fatigue failure still occurred after 107 cycles of loading, and the fatigue limit in traditional does not exist. The fatigue facture mainly located in the weld metal region at low cycle fatigue range, but in the fusion area in HCF and VHCF. Analysis of fracture surfaces analyzed by SEM revealed that the fatigue cracks initiated from welding defects such as pores, cracks and inclusions.
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Shao, Chuang, Claude Bathias, Danièle Wagner i Hua Tao. "Very High Cycle Fatigue Behavior and Thermographic Analysis of High Strength Steel". Advanced Materials Research 118-120 (czerwiec 2010): 948–51. http://dx.doi.org/10.4028/www.scientific.net/amr.118-120.948.
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Very high cycle fatigue behavior of high strength steel, were investigated using ultrasonic fatigue testing equipment at 20 kHz up to 109cycles. S-N curves at room temperature with different stress ratio (R=0.01 and R=0.1) was determined. The experimental results show that fatigue strength decrease with increasing number of cycles between 105 and 109. SEM examination of fracture surface reveals that fatigue damage was governed by the formation of cracks, and subsurface crack initiation was in the very long life range. The results shown that the portions of life attributed to subsurface crack initiation between 107 and 109 cycles are 99%.
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Zhou, Cheng En, Gui An Qian i You Shi Hong. "Fractography and Crack Initiation of Very-High-Cycle Fatigue for a High Carbon Low Alloy Steel". Key Engineering Materials 324-325 (listopad 2006): 1113–16. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.1113.
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Very-High-Cycle Fatigue (VHCF) is the phenomenon of fatigue damage and failure of metallic materials or structures subjected to 108 cycles of fatigue loading and beyond. This paper attempts to investigate the VHCF behavior and mechanism of a high strength low alloy steel (main composition: C-1% and Cr-1.5%; quenched at 1108K and tempered at 453K). The fractography of fatigue failure was observed by optical microscopy and scanning electron microscopy. The observations reveal that, for the number of cycles to fatigue failure between 106 and 4×108 cycles, fatigue cracks almost initiated in the interior of specimen and originated at non-metallic inclusions. An “optical dark area” (ODA) around initiation site is observed when fatigue initiation from interior. ODA size increases with the decrease of fatigue stress, and becomes more roundness. Fracture mechanics analysis gives the stress intensity factor of ODA, which is nearly equivalent to the corresponding fatigue threshold of the test material. The results indicate that the fatigue life of specimens with crack origin at the interior of specimen is longer than that with crack origin at specimen surface. The experimental results and the fatigue mechanism were further analyzed in terms of fracture mechanics and fracture physics, suggesting that the primary propagation of fatigue crack within the fish-eye local region is the main characteristics of VHCF.
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Wei, Kang, i Bo Lin He. "Failure Mechanism of Very High Cycle Fatigue for High Strength Steels". Key Engineering Materials 664 (wrzesień 2015): 275–81. http://dx.doi.org/10.4028/www.scientific.net/kem.664.275.
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In recent years, the core engineering components of high-speed train, automobiles and aircrafts are required to endure fatigue loads up from 108 to 1010 cycles. The present study results show that in the very high cycle fatigue (VHCF) regimes of more than 107 cycles, the fatigue failure of high strength steel materials can occur below the traditional fatigue limit, hence the VHCF investigations of high strength steels not only help to further understand the fatigue essence and mechanism, but also do research on the fatigue design and life assessment method. This paper summarizes works of VHCF researches for high strength steels in recent years, such as the characteristics of S-N curve, the observations on fish-eye, which is one of the typical characteristics of fracture surface, crack initiation, crack propagation, etc. The present work also analyzes the fatigue mechanisms and briefly discusses several factors that affect VHCF properties, such as hydrogen effect, inclusion effect, frequency effect. Some possible and prospective aspects of future researches are also proposed.
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Daniel Varecha, Slavomir Hrcek, Otakar Bokuvka, Frantisek Novy, Libor Trsko, Ruzica Nikolic i Michal Jambor. "Fatigue Safety Coefficients for Ultra – High Region of Load Cycles". Communications - Scientific letters of the University of Zilina 22, nr 4 (1.10.2020): 97–102. http://dx.doi.org/10.26552/com.c.2020.4.97-102.
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In this paper the authors introduce results from the field of the fatigue safety of selected steels in the region of ultra - high number of loading cycles. The fatigue tests were carried out at high frequency tension - compression loading (f = 20 kHz, T = 20 ± 5°, R = -1) in the region from N = 106 to N = 109 cycles. The fatigue safety coefficients were calculated by four methods (Goodman, Gerber, ASME elliptic and Soderberg). The percentage reduction of the fatigue safety coefficients (N = 109 vs. N = 106 cycles) was at Goodman, 7.99 ÷ 10.83 %, Gerber, 5.27 ÷ 8.26 %, ASME, 1.89 ÷ 6.42 % and Soderberg, 6.51 ÷ 10.25 %.
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Wu, Liang Chen, i Dong Po Wang. "Investigation of High Cycle and Low Cycle Fatigue Interaction on Fatigue Behavior of Welded Joints". Applied Mechanics and Materials 217-219 (listopad 2012): 2101–6. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.2101.
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Samples of Q345 steel welded joints were tested to failure under low cycle fatigue(LCF),high cycle fatigue(HCF) and combined fatigue(CCF) using an apparatus that is capable of providing interactive LCF/HCF loading. The stress ratio R is 0.5 and the frequency of HCF is about 19kHz. The result indicates that not only high frequency minor cycles superimposed on low frequency major cycles , but also low frequency minor cycles superimposed on high frequency major cycles can do remarkable damage to fatigue performance of welded joints. The CCF strength is characterized by amplitude envelope. If CCF fatigue life is characterized by LCF life, adverse effect of HCF component is underestimated. If CCF fatigue life is characterized by HCF life, adverse effect of LCF component is overrated.
Rozprawy doktorskie na temat "High fatigue cycles"
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Kim, Tae Hyun. "Fatigue of surface engineered steel in rolling-sliding contact". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325019.
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Simon, Julien. "Influence de micro-entailles sur le comportement en fatigue à grand nombre de cycles d'un alliage de TA6V : Comparaison avec le fretting-fatigue". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0034/document.
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Ce travail a porté sur l’influence d’entailles micrométriques sur la tenue en fatigue à grand nombre de cycles d’un alliage de titane et la comparaison avec un cas de fretting-fatigue. Des études préliminaire sont montré que des entailles micrométriques pouvaient reproduire les champs de contraintes d’essais de fretting-fatigue. Le projet COGNAC dirigé par Safran Aircraft Engines a été créé dans l’objectif d’évaluer la faisabilité d’un modèle unique capable de simuler la tenue en fatigue de pièces subissant des sollicitations de fretting ou de fatigue en présence d’entailles. Le cadre expérimental de cette thèse est limité à la partie du projet traitant des entailles. Afin d’avoir le même état de préparation de surface, les micro-entailles et les surfaces des éprouvettes de fretting fatigue sont usinées par meulage. Afin de reproduire les gradients de contraintes observés localement pour des chargements de fretting-fatigue, des entailles en V avec des rayons compris entre 50 μm à 500 μm ont été choisies.L’étude du taux de triaxialité et du cisaillement a permis de définir une géométrie d’éprouvette de comparaison avec le fretting fatigue qui comporte 2 entailles en V inclinées en face à face. Trois campagnes expérimentales de fatigue à grand nombre de cycles ont été menées. La première sur des éprouvettes lisses meulées afin d’obtenir une limite de fatigue de référence sans concentration de contraintes. La seconde sur des éprouvettes avec une entaille non inclinée ayant une profondeur de500 μm afin d’étudier les effets du rayon de fond d’entaille sur la limite de fatigue. La dernière est une campagne sur les éprouvettes avec 2 entailles inclinées qui permettent de reproduire les champs de contrainte des essais de fretting. Les premiers stades de fissuration ont été étudiés. Les facettes de pseudo clivage, la présence d’un premier stade de fissuration et les amorçages multiples en fond d’entaille ressemblent à ce qui peut être vu sur des essais de fretting. Par contre la présence de fissures non propageantes en fond d’entaille sous la limite de fatigue n’a pas pu être démontrée, alors que ces fissures non propageantes sont observables sur les essais de fretting-fatigue. Les sites d’amorçages et les mécanismes des premiers endommagements semblent être pilotés par les zones affectées par le meulage. Enfin trois critères de fatigue ont été utilisés afin de tenter de reproduire nos résultats expérimentaux. L’approche basée sur la théorie du gradient –avec un gradient local et un impact affine du gradient- et celle basée sur la théorie de la distance critique ont fourni des résultats corrects sur les éprouvettes entaillées mais ne peuvent faire le lien avec les éprouvettes sans concentrations de contraintes. Enfin, l’approche probabiliste utilisée a produit des résultats très proches des résultats expérimentaux à la fois sur des éprouvettes lisses et des micro-entailles. La comparaison des résultats expérimentaux montrent que le champ de contrainte de Crossland proche de la surface d’amorçage du fretting-fatigue est proportionnel à celui proche d’un fond d’entaille dans le cas d’une éprouvette avec 2 entailles en face à face. Le niveau de la sollicitation des 2 essais diffère localement d’environ20%. Dans la suite des travaux, il serait particulièrement intéressant de relancer une campagne de comparaison entre fretting et entailles en utilisant un critère probabiliste pour dimensionner les essais afin de proposer une méthodologie commune de prise en compte des concentrations de contraintes dans les cas de fretting-fatigue et de concentrateurs géométriques sollicités en fatigueThis study is about the influence of micro-notches on the high cycle fatigue behavior of a Ti64 alloy and the comparison with similar fretting fatigue tests. Preliminary studies showed that fretting-fatigue stress fields can be reproduced by micro-notched. The COGNAC project leaded by Safran Aircraft Engines was built to verify if a unique model can reproduce both fretting-fatigue and notched samples fatigue tests. The scope of this experimental study is limited to the notched samples. In this PHD thesis, the notches are grinded and the results are compared with fretting-fatigue tests on grinded surfaces. V-notched with notch root radius from 50 to 500 μm were chosen to reproduce the stress gradient of fretting-fatigue tests. A geometry with two inclined notches facing each other allows to reproduce shear stress and stress triaxiality from fretting-fatigue tests. Three different experimental studies were performed. First on un-notched specimens with a grinded surface state to produce a reference fatigue limit for grinded surface state without stress concentration. The second study the notch root radius effect on the fatigue limit with samples with one non-inclined notch of 500 μm of depth. The last one is a series of fatigue tests on samples with two inclined notches that reproduce the stress distribution of fretting-fatigue tests. Pseudo-cleavage facets, multi cracks initiations in the notch root and the presence of two propagation stages is similar to the fretting-fatigue tests mechanisms. However, non propagating cracks were not observe at the notch root while many of them were present during the fretting-fatigue test. The initiation sites and the early stages of propagation seem to be controlled by grinded affected areas. Finally, three fatigue criteria were used to try to reproduce the experimental results. The criteria based on the critical distance theory and gradient theory –with a local gradient and an affine effect of the gradient term- can reproduce the fatigue limits of notched samples but fail to predict both notched and un-notched specimen fatigue limits with a unique data set. The third one is a probabilistic criterion which success to predict the experimental fatigue limits not only of notched samples but also smooth ones. The comparisons between the experimental results of the fatigue on the specimens with two inclined notches and the fretting-fatigue shows a difference of 20%. The distribution of the Crossland stress is quite similar. In the future, it would be useful to make a new comparison between fretting-fatigue and fatigue on notches using the probabilistic criterion to design the tests. This new comparison could lead to the proposal of a unique methodology to take into account the fretting-fatigue and the fatigue on stress concentrators
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Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms". Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.
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Ce travail vise à améliorer notre compréhension du comportement en fatigue à grand et très grand nombre de cycles d’un acier ferrito-martensitique dual phase, notamment les effets de la température et de la vitesse de déformation résultant de chargements cycliques à haute fréquence. L'effet de la fréquence sur la réponse en fatigue de l'acier DP600 a été étudié en effectuant des essais de fatigue sur une machine ultrasonique travaillant à 20 kHz et sur une machine conventionnelle travaillant à des fréquences inférieures à 100 Hz. Des études de fractographie et des observations microscopiques à la surface des échantillons ont été effectuées pour étudier les mécanismes de déformation et de rupture. De plus, la thermographie infrarouge in situ a été utilisée pour étudier la réponse thermique et les mécanismes dissipatifs du matériau lors des essais de fatigue. Les courbes S-N ont été déterminées à partir de chargements de fatigue ultrasoniques à 20 kHz et d’essais conventionnels à 30 Hz. La durée de vie pour une amplitude de contrainte donnée est plus élevée dans le cas de la fatigue ultrasonique bien que la limite de fatigue soit identique dans les deux cas. L’augmentation inévitable de la température en fatigue ultrasonique à fortes amplitudes de contraintes, ainsi que le comportement dépendant de la vitesse de déformation de la ferrite, en tant que structure CC, ont été trouvés comme les paramètres clés expliquant le comportement observé en fatigue, et la réponse thermique sous les fréquences faibles et ultrasoniques. Les écarts observés entre l’essai de fatigue conventionnel et celui ultrasonique ont été évalués à travers les mécanismes de mobilité des dislocations vis dans la phase ferritique de structure cubique centrée (CC). La durée de vie plus élevée et l’amorçage de la fissure principale sur une inclusion observés en fatigue ultrasonique ont été attribués au vieillissement dynamique résultant du fort auto-échauffement du matériau aux fortes amplitudes de contraintes. L'existence d'une transition du régime thermiquement activé au régime athermique avec l’augmentation de l'amplitude de contrainte a été mise en évidence. Au-dessous de la limite de fatigue, la déformation a lieu dans un régime thermiquement activé alors qu'elle est dans un régime athermique au-dessus de la limite de fatigue. En fatigue conventionnelle, la déformation est athermique pour toutes les amplitudes de contrainte. Une carte de transition a été produite en utilisant les résultats expérimentaux pour l'acier DP600 ainsi que les données disponibles dans la littérature pour d'autres aciers à base de ferrite, montrant ainsi la corrélation entre le mouvement des dislocations vis thermiquement activé et l'absence de rupture en fatigue à très grand nombre de cycleThis work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue
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Tarar, Wasim Akram. "A New Finite Element Procedure for Fatigue Life Prediction and High Strain Rate Assessment of Cold Worked Advanced High Strength Steel". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204575243.
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Zhao, Mengxiong. "Ultrasonic fatigue study of Inconel 718". Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100063/document.
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L’Inconel 718 est utilisé dans les disques de turbine des moteurs d’avion, de par sa haute résistance à la corrosion, à l’oxydation, au fluage et sa haute résistance mécanique à très haute température. Le nombre total de cycles de ces composants mécaniques s’élève à 109~1010 durant sa vie. Ils subissent des chargements de grande amplitude à faible fréquence, comme les forces centrifuges ou les contraintes thermiques mais aussi des chargements de faibles amplitudes à très haute fréquence, du aux vibrations des pales. Dans ce travail, on se propose d’étudier la fatigue à très grand nombre de cycles (VHCF) de l’Inconel 718 en utilisant des machines de fatigue ultrasonique, fonctionnant à 20KHz. Le système d’acquisition utilise des cartes NI et le logiciel LabView pour superviser la fréquence, la température, les déplacements durant toute la durée des tests. Des capteurs laser Keyence utilisant deux sondes pour les faces supérieure et inférieure de l’éprouvette permettent de capturer la fréquence et les modes de vibration. La différence entre les valeurs moyennes mesurées permet d’accéder à l’allongement de l’éprouvette, dû à l’auto-échauffement.3 types de matériaux avec différents traitements thermiques, AR, DA et DAHQ de l’ONERA et SAFRAN sont comparés. La différence au niveau de la taille de grain, de la phase, des précipités, … est analysée par micrographie métallographique en utilisant un microscope optique (MO) et un microscope électronique à balayage (MEB). Le comportement en traction quasi-statique et sous chargement cyclique contrainte-déformation est aussi proposé. La transition entre durcissement et adoucissement cyclique apparait à l’issue du traitement thermique. Finalement, les surfaces de ruptures sont observées en utilisant des caméras optiques et un MEB afin d’identifier les mécanismes de ruptures de l’Inconel 718 dans le domaine de la fatigue à très grand nombre de cyclesInconel 718 is widely used in turbine disk of aeronautic engines, due to its high resistance to corrosion, oxidation, thermal creep deformation and high mechanical strength at elevated temperature. The total cycle of these mechanical components is up to 109~1010 during its whole lifetime. It endures high-amplitude low-frequency loading including centrifugal force or thermal stress, and also low-amplitude high-frequency loading came from vibration of blade.In this work, the very high cycle fatigue (VHCF) behaviour of Inconel 718 with self-heating phenomenon without any cooling is studied using ultrasonic fatigue system at 20KHz. Acquisition system is improved using NI capture card with LabView for monitoring the frequency, temperature, displacement and so on during all the tests. Keyence laser sensor with two probes at the top and bottom surfaces of the specimens is used to reveal the frequency and vibration mode. The difference of mean values between these two probes is the elongation of the specimen caused by self-heating phenomenon.Three sets of materials with different heat treatment, As-Received (AR), Directly Aged (DA) and Directly Aged High Quality (DAHQ) from ONERA and SAFRAN are compared. The difference of grain size, phase, precipitate particle, etc. is investigated by metallographic micrograph using optical microscope (OM) and scanning electron microscope (SEM). Quasi-static uniaxial tensile property and cyclic stress-strain response is also proposed. The transition from cyclic hardening to cyclic softening appears after aged heat treatment. Finally, fracture surfaces are observed using optical camera and scanning electron microscope in order to identify the mechanism of fracture of Inconel 718 in the VHCF domain
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Marti, Nicolas. "Effets de la fréquence et de la température sur les mécanismes de microplasticité en fatigue à grand et très grand nombre de cycles". Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0041/document.
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Il existe actuellement une demande croissante pour le développement de méthodes expérimentales rapides et fiables permettant d'estimer la résistance à la fatigue dans le domaine de la fatigue à grands nombres de cycles. En ce sens, la fatigue ultrasonique apparue dans les années cinquante est très intéressante pour les industriels. En effet, la fréquence typique de ces essais est de 20 kHz ce qui permet d'atteindre le domaine des très grandes durées de vie en des temps d'essais raisonnables (109 cycles sont atteints en 14 h). Cependant ces essais posent le problème de l'effet de la fréquence et plus généralement de la validité des résultats obtenus pour estimer la durée de vie de structures chargées à des fréquences très inférieures à 20 kHz. L'objectif de ce travail est d'évaluer l'effet de la fréquence du chargement sur les mécanismes précurseurs de l'initiation de fissures et plus précisément sur les mécanismes de microplasticité à l'échelle du grain. Ce travail de thèse s’intéresse au cas du cuivre pur polycristallin sollicité en traction-compression alternée et symétrique. Pour mettre en évidence un effet de la fréquence, les courbes de Wöhler ont été construites à différentes fréquences. L’étude s’est ensuite focalisée sur les mécanismes de microplasticité précurseurs de l’initiation de fissures et plusieurs critères ont été examinés : les morphologies des bandes de glissement et leurs positions en lien avec la microstructure, les seuils d’apparition des bandes de glissement, le développement de ces bandes avec le nombre de cycles, la répartition de la microplasticité dans les grains, les valeurs d’énergie dissipée au cours d’un cycle. Le glissement dévié et la production-diffusion de lacunes sont deux mécanismes qui interviennent dans la formation des bandes de glissement et des extrusions en surface. Leurs rôles respectifs sur les effets de fréquence observés sont discutésNowadays there is a growing demand for the development of fast and robust fatigue life prediction methods in the very high cycle fatigue domain. In this way, ultrasonic fatigue technique which appeared in 1950 is very interesting for manufacturers. Because the typical frequency of these tests is 20 kHz, this technique is efficient to perform tests up to a very high number of cycles in a reasonable time (109 cycles are reached in 14 h). However, the frequency domain of these fatigue tests facilities raises the issue of the effect of frequency and more generally the validity of the obtained results for estimating fatigue life of structures loaded at frequencies three or four order of magnitude below ultrasonic frequencies. The objective of this work is to evaluate the effect of the loading frequency on the precursors of fatigue damage, namely the microplasticity at the grain scale. This thesis work deals with the case of polycrystalline pure copper loaded in fully reversed tensioncompression. To show the effect of frequency, the Wöhler or S-N curves were constructed at different frequencies. Then, the study focused on the mechanisms of microplasticity preceding crack initiation and several criteria were investigated: the morphologies of the slip bands and their locations in the microstructure, the thresholds of appearance of the slip bands, the evolution of the slip bands amount with the number of cycles, the distribution of the microplasticity in the grains, the dissipated energy during a fatigue cycle. Cross slip and vacancies production and diffusion are two mechanisms which play a part in the formation of slip bands and extrusions in surface. Their respective roles on the effects of frequency observed are discussed
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Ma, Zepeng. "Fatigue models for life prediction of structures under multiaxial loading with variation in time and space". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX117/document.
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L'objet de ce travail est de proposer une approche multi-échelle de la fatigue fondée sur l'énergie, et susceptible d'estimer les durées de vie associées à des chargements multidimensionnels variables. Le fondement de la démarche consiste à supposer que l'énergie dissipée à petite échelle régit le comportement à la fatigue. À chaque point matériel, est associée une distribution stochastique de points faibles qui sont susceptibles de plastifier et de contribuer à la dissipation d'énergie sans affecter des contraintes macroscopiques globales. Ceci revient à adopter le paradigme de Dang Van en fatigue polycyclique. La structure est supposée élastique (ou adaptée) à l'échelle macroscopique. De plus, on adopte à l'échelle mésoscopique un comportement élastoplastique avec une dépendance de la fonction de charge plastique non seulement de la partie déviatorique des contraintes, mais aussi de la partie hydrostatique. On considère également un écrouissage cinématique linéaire sous l'hypothèse d'une plasticité associée. Au lieu d'utiliser le nombre de cycles comme variable incrémentale, le concept d'évolution temporelle du chargement est adopté pour un suivi précis de l'historique du chargement réel. L'effet de la contrainte moyenne est pris en compte dans la fonction de charge mésoscopique ; une loi de cumul non linéaire de dommage est également considérée dans le modèle. La durée de vie à la fatigue est ensuite déterminée à l'aide d'une loi de phénoménologique fondée sur la dissipation d'énergie mésoscopique issue du cycle d'accommodation plastique. La première partie du travail a porté sur une proposition d'un modèle de fatigie à gradient de mise en oeuvre plus simple que les précédents modèlesThe aim of this work is to propose a multi-scale approach to energy-based fatigue, which can estimate lifetimes associated with variable multidimensional loading. The foundation of the approach is to assume that the energy dissipated on a small scale governs the fatigue behavior. Each material point is associated to a stochastic distribution of weak points that are likely to plasticize and contribute to the dissipation of energy without affecting global macroscopic stresses. This amounts to adopting Dang Van's paradigm of high cycle fatigue. The structure is supposed to be elastic (or adapted) on a macroscopic scale. In addition, we adopt on the mesoscopic scale an elastoplastic behavior with a dependence of the plastic load function not only of the deviatoric part of the stresses, but also of the hydrostatic part. Linear kinematic hardening is also considered under the assumption of an associated plasticity. Instead of using the number of cycles as an incremental variable, the concept of temporal evolution of the load is adopted for a precise follow-up of the history of the actual loading. The effect of mean stress is taken into account in the mesoscopic yield function; a law of nonlinear accumulation of damage is also considered in the model. Fatigue life is then determined using a phenomenological law based on mesoscopic energy dissipation from the plastic accommodative cycle. The first part of the work focused on a proposal for a fatigue model with a simpler implementation gradient than the previous models
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Guerchais, Raphaël. "Influence d'accidents géométriques et du mode de chargement sur le comportement en fatigue à grand nombre de cycles d'un acier inoxydable austénitique 316L". Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0020/document.
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L'objectif de ces travaux de thèse est d'étudier l'influence de la microstructure et de défauts géométriques sur le comportement en fatigue à grand nombre de cycles (FGNC) d'un acier inoxydable austénitique 316L. La méthodologie proposée s'appuie sur des simulations par éléments finis (EF) d'agrégats polycristallins qui permettent de décrire les champs mécaniques à l'échelle des mécanismes impliqués dans les processus d'amorçage de fissures de fatigue.Une étude numérique préliminaire, s'appuyant sur des données expérimentales issues de la littérature, est conduite sur un cuivre électrolytique à l'aide de simulations numériques d'agrégats polycristallins en 2D. L'effet du trajet de chargement et de défauts artificiels de taille proche ou légèrement supérieure à celle de la microstructure sur les réponses mécaniques mésoscopiques sont analysés. Les capacités de prédiction de quelques critères de fatigue, s'appuyant sur des quantités mécaniques mésoscopiques, sont évaluées. Il est mis en évidence que les limites de fatigue macroscopiques prédites par un critère de fatigue probabiliste sont en accord avec les tendances expérimentales observées en fatigue multiaxiale et en présence de défauts.Une campagne expérimentale a été menée sur un acier austénitique 316L. Des essais de fatigue oligocyclique sont conduits afin de caractériser le comportement élasto-plastique du matériau. Des essais de FGNC, utilisant des éprouvettes avec et sans défaut de surface (défaut artificiel hémisphérique) ont été effectués pour estimer les limites de fatigue dans différentes conditions de sollicitation (traction, torsion, traction et torsion combinée, traction biaxiale) et pour plusieurs rayons de défaut. Dans le but de compléter la caractérisation du matériau, la microstructure est étudiée à l'aide d'analyses EBSD et la texture cristallographique est mesurée par diffraction des rayons X. Ces résultats expérimentaux sont utilisés pour reproduire, avec des simulations EF, les essais de FGNC sur des microstructures 2D et 3D représentatives de l'acier austénitique. L'hétérogénéité de quantités mécaniques mésoscopiques pertinentes en fatigue est discutée avec une attention particulière sur l'effet des défauts. L'approche probabiliste est appliquée aux résultats des modèles EF pour quantifier l'effet de la taille du défaut, pour différents trajets de chargement. La pertinence, vis-à-vis des observations expérimentales, des distributions de la limite de fatigue prédites est évaluéeThe aim of this study is to analyze the influence of both the microstructure and defects on the high cycle fatigue (HCF) behaviour of a 316L austenitic stainless steel thanks to finite element (FE) simulations of polycrystalline aggregates.%The scatter encountered in the HCF behavior of metallic materials is often explained by the anisotropic elasto-plastic behavior of individual grains leading to a highly heterogeneous distribution of plastic slip.Since fatigue crack initiation is a local phenomenon, intimately related to the plastic activity at the crystal scale, it seems relevant to rely on this kind of modeling to evaluate the mechanical quantities.A preliminary numerical study, based on experimental data drawn from the litterature, was conducted on an electrolytic copper using simulations of 2D polycrystalline aggregates. The effect of the loading path and small artificial defects on the mesoscopic mechanical responses have been analyzed separately. Moreover, the predictive capabilities of some fatigue criteria, relying on the mesoscopic mechanical responses, has been evaluated. It was shown that the macroscopic fatigue limits predicted by a probabilistic fatigue criterion are in accordance with the experimental trends observed in multiaxial fatigue or in the presence of small defects.An experimental campaign is undertaken on an austenitic steel 316L. Low cycle fatigue tests are conducted in order to characterize the elasto-plastic behavior of the material. Load-controled HCF tests, using both smooth specimens and specimens containing an artificial hemispherical surface defect, are carried out to estimate the fatigue limits under various loading conditions (tension, torsion, combined tension and torsion, biaxial tension) and several defect radii. To complete the characterization of the material, the microstructure is studied thanks to EBSD analyzes and the cristallographic texture is measured by X-ray diffraction. These experimental data are used to reproduce, with FE simulations, the HCF tests on 2D and 3D microstructures representative of the austenitic steel. The heterogeneity of the mesoscopic mechanical quantities relevant in fatigue are discussed in relation to the modeling. The results from the FE models are then used along with the probabilistic mesomechanics approach to quantify the defect size effect for several loading paths. The relevance, with respect to the experimental observations, of the predicted fatigue strength distributions is assessed
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Bracquart, Benoît. "Etude des interactions défaut géométrique / microstructure dans les mécanismes d’endommagement en fatigue à grand nombre de cycles d’alliages métalliques". Thesis, Angers, 2018. http://www.theses.fr/2018ANGE0009.
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L'objectif de ces travaux est d'étudier l'influence de la microstructure et de défauts géométriques de surface sur le comportement en fatigue à grand nombre de cycles (FGNC) d'un aluminium polycristallin de pureté commerciale. Ils s'appuient sur une campagne expérimentale de fatigue et des simulations numériques par la Méthode des Éléments Finis (MEF), afin de mieux appréhender les paramètres microstructuraux gouvernant l'amorçage de fissure aux défauts. Pour cela, les deux dimensions caractéristiques (grains et défaut) sont faites varier. Des traitements thermomécaniques sont mis ainsi en place pour contrôler la taille de grains, avant une caractérisation du comportement monotone et cyclique. Par la suite, des essais de FGNC uni-axiaux en traction-compression alternée sur éprouvettes avec défauts sont effectués, soit avec suivi de fissure de surface in-situ, soit avec étude de l'amorçage de fissure en fond de défaut après cyclage. Les résultats sont par la suite analysés afin de déterminer l'influence des différentes dimensions caractéristiques, ainsi que de l'orientation cristalline, via une campagne EBSD. Des simulations cycliques utilisant la MEF sont ensuite réalisées pour déterminer finement les champs mécaniques locaux. Ainsi, des maillages d'agrégats polycristallins 3D représentatifs des configurations expérimentales sont mis en place. Une loi de comportement de plasticité cristalline à gradient est utilisée afin de traduire le glissement plastique à l'échelle des systèmes de glissement et des effets de taille de grains. La répartition d'un indicateur de fatigue dans les différentes configurations est étudiée, afin de compléter les résultats expérimentauxThe aim of this study is to analyze the influence of microstructure and geometrical surface defects on the high cycle fatigue (HCF) behavior of acommercial purity polycrystalline aluminium. This work relies on an experimental test programme and numerical Finite Element (FE) simulations, in order to better understand microstructural parameters governing crack initiation at defects. To this end, both caracteristic dimensions (grains and defect) are varied. Thermomechanical treatments are set up to control the grain size, and obtained microstructures are caracterized monotonically and cyclically. Then, uniaxial fully reversed tension-compression HCF tests are carried out on specimens with defects, either with an in-situ surface crack monitoring, or a study of the crack initiation at the defect root after cycling. Results are then analyzed in order to determine the influence of different characteristic lengths, as well as crystalline orientation, via EBSD maps. Numerical FE simulations are then carried out to detetermine precisely local mechanical fields. To this end, polycrystalline aggregates 3D meshes representative of experimental configurations are set up. A crystal plasticity constitutive model with gradient is used in order to reproduce the plastic slip at the glide system scale, and the grain size effect. The distribution of afatigue indicator parameter in the different configurations is studied, in order to complement experimental results
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Alarcon, Tarquino Eduardo Augusto. "Structural fatigue of superelastic NiTi wires". Thesis, Brest, 2018. http://www.theses.fr/2018BRES0019/document.
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Ce travail de thèse aborde les conditions et les mécanismes qui conduisent des fils superélastiques de NiTi à la rupture sous chargement mécanique cyclique. Les alliages à mémoire de forme du type NiTi présentent des propriétés thermomécaniques fonctionnelles comme la superélasticité et l’effet de mémoire de forme simple et double, lesquels sont générées grâce aux transformations de phase martensitiques provoquées soit par un changement de la contrainte ou de la température. Ces transformations de phase sont en principe des processus totalement réversibles et sans endommagement. Cependant, lorsque le NiTi est soumis à des transformations de phase induites par des contraintes cycliques, la performance en fatigue de l’alliage chute considérablement par rapport au NiTi non-transformant. La plupart des courbes S-N de fatigue rapportant cette chute ont été mesurées sur des fils NiTi a section constante dans lesquels les transformations martensitiques se développent de façon hétérogene par nucléation et propagation de bandes de cisaillement. De plus, d'après notre expérience, des essais de fatigue sur des échantillons de fils à section constante entrainent la rupture à l'intérieur des mors de la machine d'essai. Par conséquent, les valeurs de contrainte-déformation rapportées dans les courbes S-N ne sont pas nécessairement représentatives des conditions mécaniques critiques qui conduisent le matériau à la rupture. Dans le but de mieux caractériser les performances en fatigue des fils NiTi, nous avons effectué une série de tests de fatigue en traction-traction, tout en utilisant des échantillons sous forme ≪ diabolo ≫. La géométrie de ces échantillons nous a permis de confiner tous les processus de transformation martensitique et de fatigue dans un volume utile bien défini. La caractérisation du comportement thermomécanique de ces échantillons a été réalisée en combinant plusieurs techniques expérimentales et d'analyse telles que la corrélation d'image numérique(DIC), la thermographie infrarouge, la diffraction des rayons X à source synchrotron, la microscopie optique, la microscopie électronique à balayage et l'analyse par éléments finis. Une attention particulière à été portée à la performance de NiTi dans le régime à grand nombre de cycles (HCF) dans laquelle le matériau présente un comportement élastique ou une transformation de phase intermédiaire (appelée R-phase). Les résultats des tests de fatigue nous ont permis de distinguer les étapes de nucléation et de propagation des fissures pendant la durée de vie totale de nos échantillons. Afin de mieux comprendre les mécanismes qui conduisent à la nucléation des fissures, nous avons appliqué la méthode de l’auto-échauffement, qui a démontré son efficacité dans la prédiction de fatigue dans les cas des alliages d'aluminium et des alliages d'acier. Cette méthode corrèle l'élévation de température d'un échantillon soumis à différentes amplitudes de charge cyclique avec des mécanismes de dissipation d'énergie. Ces mécanismes dissipatifs sont après associés à l’accumulation d’endommagement locale dans le matériau. La méthode d'autoéchauffement a été réalisée en utilisant des mesures de champs thermiques des d'échantillons de NiTi sous forme diabolo pendant de chargement cycliqueThis Ph.D. dissertation thesis addresses the conditions and mechanisms that lead superelastic NiTi wires to fail under cyclic mechanical loads. NiTi shape memory alloys exhibit functional thermomechanical properties (superelasticity, shape memory effect, thermal actuation) due to martensitic phase transformations caused by a change of the applied stress and temperature. These phase transformations are though as fully reversible damage-free processes, however, when NiTi is subjected to repetitive stress-induced phase transformations its fatigue performance drops drastically in comparison to non-transforming NiTi. Most of fatigue S-N curves reporting this drop were measured on straight NiTi wires in which martensitic transformations proceed heterogeneously through nucleation and propagation of shear bands. Moreover, from our experience fatigue testing straight wire samples results in undesired failure inside the testing machine clamps. Hence, the reported stress-strain values in S-N curves are not necessarily representative of the critical mechanical conditions that lead the material to failure. With the aim of better characterize the fatigue performance of NiTi wires, we started by carrying out a series of pull-pull fatigue tests using hourglass-shaped samples. This sample geometry allowed us to confine all martensitic transformation and related material fatigue processes into a well-defined gauge volume. The samples’ characterization was performed by combining several experimental and analysis techniques such as Digital Image Correlation, Infrared Thermography, Synchrotron-source X-ray diffraction, Optical Microscopy, Scanning Electron Microscopy and Finite Element Analysis. A special attention was paid to the High Cycle Fatigue (HCF) performance of NiTi in which the material shows elastic behavior and/or an intermediate phase transformation (so-called R-phase). The results from HCF tests allowed us to distinguish crack nucleation and crack propagation stages during the total life of our NiTi samples. In order to get a better understanding of the mechanisms that lead to crack nucleation, we applied the nonconventional Self-Heating fatigue assessment method, which has shown efficiency in the case of aluminum and steel alloys. This method correlates the temperature elevation of a sample subjected to different cyclic load amplitudes with energy dissipating mechanisms that contribute to accumulating local damage in the material. The Self-Heating method was performed using full-field thermal measurements of cyclically loaded NiTi hourglass-shaped samples
Książki na temat "High fatigue cycles"
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Christ, Hans-Jürgen, red. Fatigue of Materials at Very High Numbers of Loading Cycles. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3.
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Zhu, Dongming. Influence of high cycle thermal loads on thermal fatigue behavior of thick thermal barrier coatings. Washington, D.C: National Aeronautics and Space Administration, 1997.
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1947-, Miller Robert A., i United States. National Aeronautics and Space Administration. Scientific and Technical Information Program., red. Influence of high cycle thermal loads on thermal fatigue behavior of thick thermal barrier coatings. [Washington, D.C.]: National Aeronautics and Space Administration, Office of Management, Scientific and Technical Inforamtion Program, 1997.
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Van, Ky Dang, i Ioannis Vassileiou Papadopoulos, red. High-Cycle Metal Fatigue. Vienna: Springer Vienna, 1999. http://dx.doi.org/10.1007/978-3-7091-2474-1.
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Dang, Van Ky, i Papadopoulos Iōannēs V, red. High-cycle metal fatique: From theory to applications. Wien: Springer, 1999.
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Herda, D. A. A comparison of high cycle fatigue methodologies. [Marshall Space Flight Center, Ala.]: National Aeronautics and Space Administration, George C. Marshall Space Flight Center, 1992.
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Hall, Rodney H. F. Crack growth under combined high and low cycle fatigue. Portsmouth: Portsmouth Polytechnic, School of Systems Engineering, 1991.
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A, Miller Robert, i Lewis Research Center, red. Investigation of thermal high cycle and low cycle fatigue mechanisms of thick thermal barrier coatings. [Cleveland, Ohio]: National Aeronautics and Space Administration, Lewis Research Center, 1998.
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A, Miller Robert, i Lewis Research Center, red. Investigation of thermal high cycle and low cycle fatigue mechanisms of thick thermal barrier coatings. [Cleveland, Ohio]: National Aeronautics and Space Administration, Lewis Research Center, 1998.
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United States. National Aeronautics and Space Administration., red. Estimation of high temperature low cycle fatigue on the basis of inelastic strain and strainrate. [Washington, DC] : National Aeronautics and Space Administration: For sale by the National Technical Information Service, 1986.
Znajdź pełny tekst źródłaCzęści książek na temat "High fatigue cycles"
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Cao, X. J., M. R. Sriraman i Qing Yuan Wang. "Fatigue in Ti-6Al-4V at Very High Cycles". W Materials Science Forum, 259–62. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-462-6.259.
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Spriestersbach, D., P. Grad, A. Brodyanski, J. Lösch, M. Kopnarski i Eberhard Kerscher. "Very high cycle fatigue crack initiation: investigation of fatigue mechanisms and threshold values for 100Cr6". W Fatigue of Materials at Very High Numbers of Loading Cycles, 167–210. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_9.
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Weidner, Anja, Alexander Schmiedel, Mikhail Seleznev i Horst Biermann. "Influence of Internal Defects on the Fatigue Life of Steel and Aluminum Alloys in the VHCF Range". W Multifunctional Ceramic Filter Systems for Metal Melt Filtration, 605–43. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-40930-1_24.
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AbstractThis chapter concerns the influence of internal defects (i.e. nonmetallic inclusions, secondary phases and cast defects) on the fatigue lifetime of steel and aluminum alloys in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime. The detrimental effect of internal defects depends on multiple factors such as size, morphology, chemical composition, test temperature or position in the material. Specimens were tested after active and/or reactive melt filtration processes of the materials which served to influence the amount and size distribution of internal defects. Fatigue experiments up to 109 cycles were carried out using ultrasonic fatigue testing equipment. In addition, in situ methods, as e.g. full surface view thermography and acoustic emission (AE), were applied to study the processes of crack initiation and propagation, which finally lead to fatigue failure. Furthermore, the cyclically strained samples were subjected to fractographic analysis and the S–N-curves were discussed according to the characteristics of the crack-initiating defects. Based on these investigations, an enhanced knowledge about the correlation of internal defects on the materials’ fatigue strength enables a specific melt filtration strategy adjusted to the materials’ service conditions.
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Kolyshkin, A., E. Kaufmann, M. Zimmermann i H. J. Christ. "Development of a fatigue life prediction concept in the very high cycle fatigue range based on covariate microstructural features". W Fatigue of Materials at Very High Numbers of Loading Cycles, 343–64. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_16.
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Madhusoodanan, H., E. Jansen i Raimund Rolfes. "A physically based fatigue damage model for simulating three-dimensional stress states in composites under very high cycle fatigue loading". W Fatigue of Materials at Very High Numbers of Loading Cycles, 533–59. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_24.
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Grigorescu, A., P. M. Hilgendorff, Martina Zimmermann, Claus-Peter Fritzen i Hans-Jürgen Christ. "Fatigue behaviour of austenitic stainless steels in the VHCF regime". W Fatigue of Materials at Very High Numbers of Loading Cycles, 49–71. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_3.
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Lorsch, P., M. Sinapius i Peter Wierach. "Methodology for the high-frequency testing of fiber-reinforced plastics". W Fatigue of Materials at Very High Numbers of Loading Cycles, 487–509. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_22.
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Ritz, F., T. Beck i S. Kovacs. "Fatigue behavior of X10CrNiMoV12-2-2 under the influence of mean loads and stress concentration factors in the very high cycle fatigue regime". W Fatigue of Materials at Very High Numbers of Loading Cycles, 253–72. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_12.
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Bach, J., M. Göken i Heinz-Werner Höppel. "Fatigue of low alloyed carbon steels in the HCF/VHCF-regimes". W Fatigue of Materials at Very High Numbers of Loading Cycles, 1–23. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_1.
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Burkart, Klaus, B. Clausen i H. W. Zoch. "Evaluation of multiple-flaw failure of bearing steel 52100 of different heats in the VHCF regime and mathematical determination of single-flaw behaviour". W Fatigue of Materials at Very High Numbers of Loading Cycles, 211–31. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_10.
Pełny tekst źródłaStreszczenia konferencji na temat "High fatigue cycles"
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Holycross, Casey M., M. H. Herman Shen, Onome E. Scott-Emuakpor i Tommy J. George. "Energy-Based Fatigue Life Prediction for Combined Low Cycle and High Cycle Fatigue". W ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95785.
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Gas turbine engine components are subjected to both low and high cycle fatigue as a result of mechanical and vibrational loading. Mechanical loading is generally within the low cycle fatigue regime and attributed to throttle up/throttle down cycles of various flight maneuvers or engine start-up/shut-down cycles over the course of a component’s lifetime. Vibrational loading causes high cycle fatigue of a multiaxial stress state, and is attributed to various forced and free vibration sources manifested as high order bending or torsion modes. Understanding the interaction of these two fatigue regimes is necessary to develop robust design techniques for gas turbine engines and turbomachinery in general. Furthermore, applying a method to accurately predict fatigue performance from a reduced data set can greatly reduce time and material costs. This study investigates commonly used fatigue life prediction models and techniques in their ability to accurately model fatigue lives of Al 6061-T651 cylindrical test specimens subjected to various stress ratios, mean stresses, and high cycle/low cycle interaction. Comparisons between these models are made and modifications are proposed than can account for these complex loading effects where appropriate.
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Ranganath, Sampath, Hardayal S. Mehta, Nathan A. Palm i John Hosler. "Proposed ASME Code High Cycle Fatigue Design Curves for Austenitic and Ferritic Steels". W ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-66242.
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The ASME Code fatigue curves (S–N curves) are used in the fatigue evaluation of reactor components. For the assessment of high frequency cyclic loading (such as those produced by flow-induced vibrations), where the number of cycles is expected to be very large and cannot be estimated, the stresses are evaluated by comparison with the fatigue limit1 at 1011 cycles. Other high cycle events of finite time duration (e.g. safety relief loading), where the number of cycles is large but well defined, the fatigue evaluation is performed by comparing the calculated stress with the allowable values defined by the high cycle fatigue design curve. This paper discusses the development of fatigue design curves for austenitic and ferritic steels when the number of cycles is in the range 106 – 1011 cycles. The first part of the paper addresses austenitic stainless steel components which are used for reactor internals. Specifically, the approach described here uses temperature dependent properties (cyclic yield strength, cyclic ultimate strength) for the mean stress correction and the correction for the modulus of elasticity. The high cycle fatigue design curve is developed by applying the mean stress and the E correction on the reversing load mean data curve and applying a factor of 2 on stress. The generic methodology developed for austenitic steel was applied to carbon and low alloy steels also. The proposed fatigue design curves are part of a draft ASME Code Case being considered by the ASME Code Subgroup on Design Methods. This paper describes the technical basis for the proposed ASME Code Case for the high cycle fatigue design curves for austenitic and ferritic steels.
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Matsumori, Yoshiaki, Jumpei Nemoto, Yuji Ichikawa, Isamu Nonaka i Hideo Miura. "High Cycle Fatigue Properties of Modified 9Cr-1Mo Steel at Elevated Temperatures". W ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-87329.
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Since high-cycle fatigue loads is applied to the pipes in various energy and chemical plants due to the vibration and frequent temperature change of fluid in the pipes, the high-cycle fatigue behavior of the alloys used for pipes should be understood quantitatively in the structural reliability design of the pipes. The purpose of this study, therefore, is to clarify the high-cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel at temperatures higher than 400°C. This material is one of the effective candidates for the pipes in fast breeder demonstration reactor systems. A rotating bending fatigue test was applied to samples at 50 Hz in air. The stress waveform was sinusoidal and the stress ratio was fixed at −1. The fatigue limit was observed at room temperature and it was about 420 MPa. This value was lower than the 0.2% proof stress of this alloy by about 60 MPa. This decrease can be attributed to the cyclic softening of this material. The limited cycles at knee point was about 8×105 cycles. All fracture was initiated from a single surface crack and no inclusion-induced fracture was observed in the fracture surface by SEM. Thus, the high-cycle fatigue design based on the fatigue limit may be applicable to the modified 9Cr-1Mo steel at room temperature. The fatigue limit of about 350 MPa was also observed at 400°C, and it appeared at about 107 cycles, while it appeared at around 106 cycles at room temperature. Thus, it was confirmed that the fatigue strength of this alloy decrease with temperature. However, the fatigue limit didn’t appear at 550°C up to 108 cycles. The fatigue limit may disappear in this alloy at 550°C. It is very important, therefore, to evaluate the ultra-high cycle fatigue strength of this alloy at temperatures higher than 400°C.
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Lanning, David B., George K. Haritos i Theodore Nicholas. "High Cycle Fatigue Behavior and Notch Size Effects in Ti-6Al-4V". W ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1137.
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Abstract The notch size effect of forged Ti-6Al-4V plate, loaded under high cycle fatigue (HCF) conditions, is investigated for both cylindrical and flat fatigue specimens. Cylindrical specimens were machined with three sizes of circumferential V-notches, with the smallest size dictated by the ability to machine within given tolerances. Flat dogbone specimens were machined with two sizes of opposite V-notches. All notches in both cylindrical and flat specimens have an elastic stress concentration factor of approximately Kt = 2.7. The state of stress at the notch root in the cylindrical specimens is biaxial. Thin flat specimens were chosen with the intent of minimizing the out-of-plane (through the thickness) stress component at the notch root. All specimens were cycled to obtain points on a Haigh diagram, also referred to as the modified Goodman diagram, for a constant life of 106 fatigue cycles. Specimens were cycled at stress ratios of R = 0.1, 0.5, and 0.8, at a frequency of 50 Hz. A step loading technique for generating a point on the Haigh diagram from a single test specimen was used, where the fatigue limit is found by fatiguing the specimen for 106 cycles at a stress level below which failure is expected. If failure does not occur, the stress level is raised and the specimen again fatigued for 106 cycles. This procedure is repeated until failure, after which the fatigue limit is calculated by interpolation. The validity of this technique for Ti-6Al-4V was demonstrated by generating constant amplitude stress-life data for comparison with the interpolated fatigue limits. The notch size effect is examined in light of the stress state at the notch root, and the appropriateness of the von Mises effective stress in characterizing the multiaxial state of stress in HCF is considered.
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El-Sayed, Mohamed E. M. "Transition From Low Cycle to High Cycle in Uniaxial Fatigue". W ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66202.
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Fatigue is the most critical failure mode of many mechanical component. Therefore, fatigue life assessment under fluctuating loads during component development is essential. The most important requirement for any fatigue life assessment is knowledge of the relationships between stresses, strains, and fatigue life for the material under consideration. These relationships, for any given material, are mostly unique and dependent on its fatigue behavior. Since the work of Wöhler in the 1850’s, the uniaxial stress versus cycles to fatigue failure, which is known as the S-N curve, is typically utilized for high-cycle fatigue. In general, high cycle fatigue implies linear elastic behavior and causes failure after more than 104 or 105 cycles. However. the transition from low cycle fatigue to high cycle fatigue, which is unique for each material based on its properties, has not been well examined. In this paper, this transition is studied and a material dependent number of cycles for the transition is derived based on the material properties. Some implications of this derivation, on assessing and approximating the crack initiation fatigue life, are also discussed.
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Wang, Xiaozhi, Joong-Kyoo Kang, Yooil Kim i Paul H. Wirsching. "Low Cycle Fatigue Analysis of Marine Structures". W 25th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/omae2006-92268.
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There are situations where a marine structure is subjected to stress cycles of such large magnitude that small, but significant, parts of the structural component in question experiences cyclic plasticity. Welded joints are particularly vulnerable because of high local stress concentrations. Fatigue caused by oscillating strain in the plastic range is called “low cycle fatigue”. Cycles to failure are typically below 104. Traditional welded joint S-N curves do not describe the fatigue strength in the low cycle region (< 104 number of cycles). Typical Class Society Rules do not directly address the low cycle fatigue problem. It is therefore the objective of this paper to present a credible fatigue damage prediction method of welded joints in the low cycle fatigue regime.
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Ochi, Motoyuki, Ken Suzuki, Isamu Nonaka i Hideo Miura. "High Cycle Fatigue Strength of Modified 9Cr-1Mo Steel at Elevated Temperatures". W ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36865.
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In order to clarify the characteristics of high-cycle fatigue of the modified 9Cr-1Mo steel, a high temperature rotary bending test was carried out. As a result, the fatigue strength of this alloy decreased monotonically at elevated temperatures. It decreased from 440 MPa at room temperature to about 350 MPa at 400°C. This decrease of the fatigue strength was attributed to the temperature dependence of the yielding strength of this alloy. The fatigue limit appeared near 107 cycles at 400°C, whereas it appeared around 106 cycles at room temperature. The most important result is that the fatigue limit disappeared up to 108 cycles at temperatures higher than 500°C. Thus, the number of cycles at which the fatigue limit appeared shifted to higher cycles with increasing the testing temperature. Clear striation was observed in the stable crack growth region on the fracture surface of all the specimen tested at room temperature, 400°C, 500°C, 550°C, and 600°C. Intergranular cracking, which have been observed in creep-fatigue tests, was not observed. Since the estimated operating temperature of FBR is 550°C, it is very important to consider this fatigue strength in the structural and reliability design of the modified 9Cr-1Mo steel. In this study, the change of crystallinity of this alloy under fatigue loading was also analyzed by applying an EBSD method. The image quality (IQ) value obtained from the analysis was used for the quantitative evaluation of the crystallinity in the area where an electron beam of 20 nm in diameter was irradiated. The quality of the atomic alignment was found to degrade under the cyclic loading, and a crack started to occur on the surface of the alloy when the quality of the atomic alignment decreased to a certain critical value.
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Schuler, Xaver, Tim Schopf, Tilmann Beck, Marek Smaga, Tobias Daniel, Jürgen Rudolph i Birgit Buchholz. "Investigation of the Fatigue Behavior of Austenitic Stainless Steels and Their Welds for Reactor Internals Under Combined Low Cycle (LCF), High Cycle (HCF) and Very High Cycle (VHCF) Operational Loading Conditions". W ASME 2018 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/pvp2018-85028.
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The fatigue assessment of safety relevant components is of importance for ageing management with regard to safety and reliability of nuclear power plants. Reactor internals are subjected to thermo-mechanical fatigue induced by operational temperature transients and to flow induced vibrations. The resulting complex loading collectives induce low cycle (LCF), high cycle (HCF) and even very high cycle (VHCF) fatigue and their interaction. The existing methodological gaps within the current fatigue assessment approach are to be closed. Design code fatigue analyses use defined loads and frequencies of occurrence (specified or measured). High cycle and very high cycle fatigue loadings are not explicitly considered except for endurance limit studies of reactor internals. Furthermore, design fatigue curves in the applicable international design codes were extended by extrapolation from originally 106 up to 1011 load cycles. However, the existing data base for load cycles equal to or above 107 is still highly insufficient. The cyclic deformation behavior of the material in question (austenitic stainless steel 1.4550) is different depending on the fatigue regime respectively the applied load or deformation amplitude. While the LCF behavior is already well investigated and the basic behavior in the HCF regime is fairly well known the VHCF cyclic deformation behavior has not been characterized in sufficient detail so far. As a consequence, the real damage accumulation of variable amplitude combinations consisting of LCF- and HCF/VHCF loads is still widely unknown. A new cooperative R&D project of MPA Stuttgart, TU Kaiserslautern and Framatome GmbH addresses the existing gaps of knowledge presented above and has recently been launched. The scheduled first phase of the project will entail the following key items: • Substantiation of the threshold strain amplitude εa ≥ 0.1% for the consideration of Environmentally Assisted Fatigue (EAF) conditions in the HCF regime; • Basic characterization of the HCF and VHCF fatigue behavior at relevant operational temperatures in air at 106 − 1010 load cycles; • Fatigue behavior at variable amplitude loading (combination of LCF / HCF and LCF / VHCF); • Fatigue behavior of welds in the region of high numbers of load cycles (HCF regime > 105 load cycles and VHCF > 107); • Validation of the existing design and assessment procedures (base material and welded material); • Development of a fatigue assessment methodology for reactor internals under consideration of the transient endurance limit and damage accumulation effects. A later second phase of the project will concentrate on the following items: • Examination of the fatigue behavior of welded specimens and representative components; • Consolidation of the design process from laboratory specimen to real structures and components; • Examination of the operational loading characteristics of reactor internals with respect to dominant loadings; • Probabilistic consideration of the influence of fatigue assessment on the plant risk (core damage). The project structure will be discussed in detail in the paper.
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Whaley, P. W., L. A. Killingsworth i T. D. Bow. "Low – Cost, Accelerated High-Cycle Fatigue Testing by Resonant Dwell". W ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85680.
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Characterization of the fatigue properties of new materials using conventional empirical procedures will be very expensive and time-consuming because of the need for sufficient fatigue life data, especially in the high cycle fatigue (HCF) region. Fatigue specimens tested at 30 Hz require over nine hours to accumulate 106 cycles for each fatigue data point. Resonant-dwell double-cantilever beam specimens resonating at approximately 260 Hz accumulate 106 cycles in about an hour. This paper describes low–cost, accelerated HCF fatigue testing using resonant – dwell specimens and a small, inexpensive electrodynamic shaker. Using this method, HCF data needed for characterizing the fatigue properties of new materials can be collected about nine times faster than a servo–hydraulic test machine operating at 30 Hz.
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Schopf, T., S. Weihe, T. Daniel, M. Smaga, T. Beck i J. Rudolph. "Fatigue Behavior and Lifetime Assessment of the Austenitic Stainless Steel AISI 347 and its Associated Filler Metal ER 347 Under Low-, High- and Very High Cycle Fatigue Loadings". W ASME 2021 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/pvp2021-62005.
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Abstract The fatigue assessment of safety relevant components is of importance for ageing management with regard to safety and reliability. Those components are subjected to low cycle (LCF), high cycle (HCF), very high cycle fatigue (VHCF) and their combination in terms of complex loading collectives and nonlinear fatigue damage accumulation. Reactor internals, for example, are subjected to thermo-mechanical fatigue induced by operational temperature transients such as stratification loads and to flow induced vibrations. Obviously, methodological gaps within the current fatigue assessment approach, i.e. the assessment of the VHCF behavior, the treatment of the fatigue damage accumulation in combination with the transient endurance limit are to be bridged. Additionally, environmentally assisted fatigue is to be considered properly. Design fatigue curves in international design codes were extended from originally 106 up to 1011 load cycles. Nevertheless, the existing data base for load cycles above ≈ 107 is still insufficient. The cyclic deformation behavior of the material under discussion (AISI 347 within the recent project and AISI 304 within a follow-up project) is different depending on the fatigue regime respectively to the applied load or deformation amplitude. While the LCF behavior is already well investigated and the basic behavior in the HCF regime is fairly well known the VHCF cyclic deformation behavior has not been characterized so far. As a consequence, the real damage accumulation of variable amplitude combinations consisting of LCF- and HCF/VHCF loads is still widely unknown. A cooperative R&D project of MPA Stuttgart, WKK University of Kaiserslautern and Framatome GmbH addresses the existing gaps of knowledge discussed above and has recently been finished. The following topics will be discussed in detail in the paper: • Basic characterization of the HCF and VHCF behavior at relevant operational temperatures in air at 106 – 2·109 load cycles (base material and welded material) • Fatigue behavior at variable amplitude loading (combination of LCF / HCF and LCF / VHCF) • Numerical simulations and fatigue assessment of VHCF-regime loadings • Development of a fatigue assessment methodology under consideration of the transient endurance limit and damage accumulation effects including assessment and adaptation of appropriate fatigue damage parameters
Raporty organizacyjne na temat "High fatigue cycles"
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Andrews. L51847 Fatigue Strength of Seamless Line Pipe and Modern ERW Line Pipe. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), wrzesień 2001. http://dx.doi.org/10.55274/r0010430.
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To resolve the question as to whether or not ERW pipe might prove inferior to seamless pipe in terms of resistance to cyclic stresses, the PRCI member companies decided to fund the project described herein to assess the performance of ERW pipe versus seamless pipe. Presented herein are the results of a research project on the serviceability of seamless line pipe and modern high-frequency-welded ERW (electric-resistance-welded) line pipe. Full-scale samples of both kinds of pipe were subjected in a laboratory environment to pressure cycles simulating hundreds of years of service. Four samples of ERW pipe and one sample of seamless pipe were tested. Each sample consisted of a 20-foot length of the material fabricated with end caps. Coupons were cut from the remaining pieces to accommodate tensile and impact tests and base-metal metallography. The 20-foot specimens were subjected to pressure cycles ranging from a minimum of 100 psig to the pressure level corresponding to 46 percent of the measured ultimate tensile strength of the material.
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Hajj, Ramez, Marshall Thompson, Renan Santos Maia, Yuija Lu, Abhilash Vyas, Babak Asadi i Bibek Regmi. Updates to Mechanistic-Empirical Design Inputs for Illinois Flexible Pavements. Illinois Center for Transportation, maj 2024. http://dx.doi.org/10.36501/0197-9191/24-010.
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This study reviews the Illinois Department of Transportation’s full-depth asphalt, limiting strain criterion, and asphalt over rubblized concrete design procedures, considering technological advancements in hot-mix asphalt—namely, the increased use of recycled materials and modified asphalt binders. The researchers evaluated the current |E*| algorithm by conducting laboratory tests with four mix designs and seven asphalt binders of different Superpave performance grades. They compared predictive models, including the current Illinois modulus algorithm as well as the Witczak, Hirsch, and newly developed Illinois Center for Transportation (ICT) Bayesian neural network (BNN) models. The ultrasonic pulse velocity (UPV) nondestructive test for modulus and field modulus measurements was evaluated as well. Subsequent tasks involved reviewing current fatigue endurance limit (FEL) criteria from an adapted protocol for the four-point bending beam fatigue test. This study found that typical hot-mix asphalt modulus values in Illinois are underestimated compared to modern mixes, suggesting potential savings by allowing an increased modulus value to be used, reducing layer thickness design. Low-temperature performance grades significantly influenced modulus, and the developed ICT BNN predictive model outperformed traditional ones. While UPV was promising for modulus screening, challenges related to material properties assumptions were identified. The current stage of research on assessing modern mixes’ FEL reveals the complexity of observing FEL using simplified methods. To advance this objective, a concept of acceptable stiffness ratio (SR) is introduced. In these cases, exceptionally long fatigue life would be obtained for mixes that demonstrate an acceptable drop in SR within 10,000 cycles, with no apparent evolution of the damage state. The most conservative estimation of strain level that would result in acceptable SR aligned with IDOT’s current 70 microstrain FEL criteria. On the less conservative side, allowing a 10% drop in SR within 10,000 loading cycles could increase the acceptable SR < 1 strain level as high as approximately 180 microstrain, with caution needed regarding evolving mobility trends and environmental stressors including the changing climate.
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Davidson, David L. Damage Mechanisms in High Cycle Fatigue. Fort Belvoir, VA: Defense Technical Information Center, styczeń 1999. http://dx.doi.org/10.21236/ada359744.
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Chen, Weixing. PR-378-083601-R02 Effect of Pressure Fluctuations on Growth Rate of Near-Neutral pH SCC. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), sierpień 2017. http://dx.doi.org/10.55274/r0011010.
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This report summarizes the work completed in Phase 1 and Phase 2 of PRCI SCC-2-12 project: Effect of Pressure Fluctuations on Growth Rate of Near-Neutral pH SCC. The following two insights from the two-phase PRCI SCC 2-12 project can be proven to be the most important: 1) The identification of three types of pressure fluctuations and their different susceptibility to crack growth; 2) The importance of load interaction effects during variable amplitude pressure fluctuations in the prediction of crack growth rate. The work has enabled us to divide near-neutral pH SCC cracking into the following two governing processes: the dissolution growth process for crack initiation and early stage crack growth and the hydrogen facilitated fatigue growth after crack initiation and dormancy. The first process features very high rate of dissolution at the pipe surface caused by various forms of galvanic processes and reduced crack growth in the depth direction leading to crack dormancy. The hydrogen facilitated fatigue growth process has been determined to be predominant for the crack growth after crack initiation and dormancy. Depending on the location of pipeline sections, the pressure fluctuations could be characterized into three types based on the relative pressure levels of the large loading events and the minor cycles. It has been determined from extensive experimental investigations that crack growth under Type I pressure fluctuations with frequent underload cycles, which is often found within 30 km downstream of a compressor station, can be enhanced significantly because of effects of load interactions of variable amplitude of cyclic loading. The load-interactions during SCC of pipeline steels in near-neutral pH environments are complex, which include both the time independent load-history interactions and the time dependent load interactions related to the rate of diffusion of hydrogen and hydrogen embrittlement in response to various scenarios of pressure fluctuations. Based on the experimental findings obtained, strategies for mitigating near-neutral pH crack initiation and crack growth during field operations have been proposed. The experimental findings have also been integrated into a software, namely the Pipe-Online, for making crack growth and remaining life prediction. For the purpose of capturing all the crack-growth contributing events of pressure fluctuations for life predictions, a method of recording pressure fluctuations has also been developed.
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Gallagher, J. P., R. H. van Stone, R. E. deLaneuville, P. Gravett i R. S. Bellows. Improved High-Cycle Fatigue (HCF) Life Prediction. Fort Belvoir, VA: Defense Technical Information Center, styczeń 2001. http://dx.doi.org/10.21236/ada408467.
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Shockey, Donald A., Takao Kobayashi, Naoki Saito, Jean-Marie Aubry i Alberto Grunbaum. Fractographic Analysis of High-Cycle Fatigue in Aircraft Engines. Fort Belvoir, VA: Defense Technical Information Center, styczeń 2000. http://dx.doi.org/10.21236/ada386670.
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Bartsch, Thomas M. High Cycle Fatigue (HCF) Science and Technology Program, 2001 Annual Report. Fort Belvoir, VA: Defense Technical Information Center, maj 2002. http://dx.doi.org/10.21236/ada408071.
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Feng, Jinwei, Ricardo Burdisso, Wing Ng i Ted Rappaport. Turbine Engine Control Using MEMS for Reduction of High Cycle Fatigue. Fort Belvoir, VA: Defense Technical Information Center, marzec 2001. http://dx.doi.org/10.21236/ada387429.
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Lin, T. H. Development of a Micromechanic Theory of Crack Initiation Under High-Cycle Fatigue. Fort Belvoir, VA: Defense Technical Information Center, wrzesień 1999. http://dx.doi.org/10.21236/ada368833.
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Troiano, E., J. H. Underwood, D. Crayon i R. T. Abbott. Low Cycle Notched Fatigue Behavior and Life Predictions of A723 High Strength Steels. Fort Belvoir, VA: Defense Technical Information Center, kwiecień 1995. http://dx.doi.org/10.21236/ada299469.
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