Literatura académica sobre el tema "Creep-induced damage mechanism"
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Artículos de revistas sobre el tema "Creep-induced damage mechanism"
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Liu, Jifeng y Huizhi Zhang. "Water Content Influence on Properties of Red-Layers in Guangzhou Metro Line, China". Advances in Materials Science and Engineering 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/4808909.
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In order to reveal water content influence on shear strength, swelling, and creep properties of red-layers in Guangzhou Metro, Southern China, the typical red-layers rock and soil specimens were experimentally studied by direct shear test, UU triaxial test, swelling test, and creep test, and the measured data were analyzed. The results showed that soil internal friction angle exponentially decreased with the water content increase and cohesion in accordance with the Gaussian function firstly increased and then decreased with the increase of water content. Expansion rate significantly decreased with the initial water content increase. The red sandstone had very strong isotropic expansion and disintegration properties. The mechanism of water content effect on red-layers properties was water induced microstructures and mineral compositions change which caused the macro physical and mechanical characteristics degradation. The results should provide the reference for further research for water induced damage mechanism or creep damage control of red-layers in engineering practice.
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Leng, Dingxin, Kai Xu, Liping Qin, Yong Ma y Guijie Liu. "A Hyper-Elastic Creep Approach and Characterization Analysis for Rubber Vibration Systems". Polymers 11, n.º 6 (4 de junio de 2019): 988. http://dx.doi.org/10.3390/polym11060988.
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Rubber materials are extensively utilized for vibration mitigation. Creep is one of the most important physical properties in rubber engineering applications, which may induce failure issues. The purpose of this paper is to provide an engineering approach to evaluate creep performance of rubber systems. Using a combination of hyper-elastic strain energy potential and time-dependent creep damage function, new creep constitutive models were developed. Three different time-decay creep functions were provided and compared. The developed constitutive model was incorporated with finite element analysis by user subroutine and its engineering potential for predicting the creep response of rubber vibration devices was validated. Quasi-static and creep experiments were conducted to verify numerical solutions. The time-dependent, temperature-related, and loading-induced creep behaviors (e.g., stress distribution, creep rate, and creep degree) were explored. Additionally, the time–temperature superposition principle was shown. The present work may enlighten the understanding of the creep mechanism of rubbers and provide a theoretical basis for engineering applications.
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Chan, K. S., N. S. Brodsky, A. F. Fossum, D. E. Munson y S. R. Bodner. "Creep-Induced Cleavage Fracture in WIPP Salt Under Indirect Tension". Journal of Engineering Materials and Technology 119, n.º 4 (1 de octubre de 1997): 393–400. http://dx.doi.org/10.1115/1.2812275.
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The phenomenon of cleavage fracture initiation in rock salt undergoing concurrent creep was studied experimentally using the Brazilian indirect tension test technique. The tensile creep and cleavage fracture behaviors were characterized for rock salt from the Waste Isolation Pilot Plant (WIPP) site. The Brazilian test consists of a compressive line load applied diametrically on a disk specimen to produce a region of tensile stress in the center of the disk. The damage processes were documented using video photography. The experimental results were analyzed in terms of a wing-crack fracture model and an independently developed, coupled time-dependent, mechanism-based constitutive model whose parameters were obtained from triaxial compression creep tests. Analytical results indicate that coupling between creep and cleavage fracture in WIPP salt results in a fracture behavior that exhibits time-dependent characteristics and obeys a failure criterion involving a combination of stress difference and tensile stress. Implications of creep-induced cleavage fracture to the integrity of WIPP structures are discussed.
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Bao, Yi Wang y Yan Chun Zhou. "Bending Creep and Stress Relaxation of Ti3AlC2 at High Temperature". Key Engineering Materials 280-283 (febrero de 2007): 1373–78. http://dx.doi.org/10.4028/www.scientific.net/kem.280-283.1373.
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Creep and stress relaxation of Ti3AlC2 were investigated using three-point bending tests at 800-1200°C under various load levels. The results show that the creep rate significantly increases with increasing temperature in the rang of 1000-1200°C. Subcritical crack growth during the creep process was found to be the main failure mechanism, i.e., the stress intensity factor increases with the creep-induced crack growth and results in the ultimate fracture. The lower limit of stress relaxation was considered as the threshold value of zero-creep stresses, and the ratio of the threshold stress to the applied stress was defined to be a parameter of creep resistance for estimating deformation behavior at high temperature. SEM examination confirmed that the creep failure in Ti3AlC2 was governed by such a damage evolution: cavitation ® crack initiation ® crack extension ® fracture.
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Wang, Yang-Yang, Chen Jia, Morteza Tayebi y Bejan Hamawandi. "Microstructural Evolution during Accelerated Tensile Creep Test of ZK60/SiCp Composite after KoBo Extrusion". Materials 15, n.º 18 (16 de septiembre de 2022): 6428. http://dx.doi.org/10.3390/ma15186428.
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In the current study, the creep properties of magnesium alloy reinforced with SiC particles were investigated. For this purpose, ZK60/SiCp composite was produced by the stir casting method following the KoBo extrusion and precipitation hardening processes. The creep tests were performed at 150 °C under 10–110 MPa. The results showed that the stress exponent (n) and the average true activation energy (Q) was changed at high stresses, was found with increasing stress, the creep mechanism changing from grain boundary sliding to dislocation climb. The results of microstructure characterization after the creep test showed that at low stresses, the dynamic recrystallization resulting from twinning induced the GBS mechanism. However, at high stresses, with increasing diffusion rates, conditions are provided for dynamic precipitation and the dislocation climb of the dominant creep mechanism. Examination of the fracture surfaces and the surrounding areas showed that the cavity nucleation in the ternary boundary and surrounding precipitation was the main cause of damage. The evaluation of the samples texture after creep showed that the unreinforced alloy showed a moderately strong fiber texture along the angle of ϕ1 = 0–90°, which was tilted about Φ = 10°. A new strong texture component was observed at (90°, 5°, 0°) for the composite sample, which crept due to minor splitting of the basal pole by ~5° toward RD.
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Khan, Talha H., Michael T. Myers, Lori Hathon y Gabriel C. Unomah. "Time-Scaling Creep in Salt Rocks for Underground Storage". Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description 64, n.º 6 (1 de diciembre de 2023): 954–69. http://dx.doi.org/10.30632/pjv64n6-2023a10.
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Salt is an elastoviscoplastic material that exhibits time-dependent deformation (creep). Experimental measurements of salt creep behavior help predict underground gas repositories’ long-term geomechanical behavior. Previous time-scaling creep experiments have focused on the axial strain of unconsolidated sands. i.e., time-scaling creep effects under zero lateral strain conditions without describing the creep behavior of the radial strain. In addition, the time-scaling creep of the radial and axial strain has not been investigated in salts. A comparative testing procedure and analysis method was conducted on Spindletop salt plugs using triaxial tests for multistage triaxial tests (MST) and different holding time durations and stress regimes, resulting in time-dependent strain responses (creep tests). The MST showed evolving deformational mechanisms under the mapped yield surface based on the irrecoverable to recoverable strain ratio beginning with crack closure or conformance, plasticity, and ending at early crystal surface failure. Unlike unconsolidated sands, salts showed both time and strain amplitude scaling. The axial and radial strain data show scaling behavior under low and high levels of deviatoric stress separated by a transitional period. The salt showed only an axial creep response at low deviatoric stress distally from the yield surface (one-dimesional (1D) response or zero lateral strain), which indicates negative dilatant deformation or uniaxial compaction. In contrast, the salts showed equal strain amplitude scaling factors both axially and radially at high deviatoric stress proximal to the yield surface (two-dimensional (2D) response or unconstrained boundary condition), which suggests positive dilatant deformation. Microstructural images showed accumulated creep damage under high deviatoric stress associated with parallel planes of dislocation-intergranular slip, microcracking, and compaction-induced dilational strains. The period of scaling is interpreted as regions where a single mechanism is dominating. Strain amplitude scaling for both low and high deviatoric creep stress tests provides inputs for a constitutive model of creep response in understanding the magnitude of mechanical damage associated with time-independent stress-strain curves in salts for the structural integrity of salt caverns during cyclic fluid injection and depletion.
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Jazaeri, Hedieh, P. Bouchard, Michael Hutchings, Mike Spindler, Abdullah Mamun y Richard Heenan. "An Investigation into Creep Cavity Development in 316H Stainless Steel". Metals 9, n.º 3 (12 de marzo de 2019): 318. http://dx.doi.org/10.3390/met9030318.
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Creep-induced cavitation is an important failure mechanism in steel components operating at high temperature. Robust techniques are required to observe and quantify creep cavitation. In this paper, the use of two complementary analysis techniques: small-angle neutron scattering (SANS), and quantitative metallography, using scanning electron microscopy (SEM), is reported. The development of creep cavities that is accumulated under uniaxial load has been studied as a function of creep strain and life fraction, by carrying out interrupted tests on two sets of creep test specimens that are prepared from a Type-316H austenitic stainless steel reactor component. In order to examine the effects of pre-strain on creep damage formation, one set of specimens was subjected to a plastic pre-strain of 8%, and the other set had no pre-strain. Each set of specimens was subjected to different loading and temperature conditions, representative of those of current and future power plant operation. Cavities of up to 300 nm in size are quantified by using SANS, and their size distribution, as a function of determined creep strain. Cavitation increases significantly as creep strain increases throughout creep life. These results are confirmed by quantitative metallography analysis.
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Puzrin, Alexander M., Thierry Faug y Itai Einav. "The mechanism of delayed release in earthquake-induced avalanches". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, n.º 2227 (julio de 2019): 20190092. http://dx.doi.org/10.1098/rspa.2019.0092.
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Snow avalanches can be triggered by strong earthquakes. Most existing models assume that snow slab avalanches happen simultaneously during or immediately after their triggering. Therefore, they cannot explain the plausibility of delayed avalanches that are released minutes to hours after a quake. This paper establishes the basic mechanism of delays in earthquake-induced avalanche release using a novel analytical model that yields dynamics consistent with three documented cases, including two from Western Himalaya and one from central Italy. The mechanism arises from the interplay between creep, strain softening and strain-rate sensitivity of snow, which drive the growth of a basal shear fracture. Our model demonstrates that earthquake-triggered delayed avalanches are rare, yet possible, and could lead to significant damage, especially in long milder slopes. The generality of the model formulation opens a new approach for exploring many other problems related to natural slab avalanche release.
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Chen, Xingzhou, Quan Zhang, Xinchao Ding, Lili Chen, Wei Du, Hai Jiang y Sheng Gong. "Study on the Creep Characteristics and Fractional Order Model of Granite Tunnel Excavation Unloading in a High Seepage Pressure Environment". Sustainability 15, n.º 5 (3 de marzo de 2023): 4558. http://dx.doi.org/10.3390/su15054558.
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The creep associated with unloading surrounding rock during the excavation of deep tunnels seriously affects the stability of the tunnel, and a high seepage pressure will aggravate the strength attenuation and structural deterioration of the surrounding rock. Based on the background of the excavation-induced unloading of the surrounding rock of a deeply buried granite tunnel with high seepage pressure, in this paper we carry out a triaxial unloading seepage creep test that considers the effects of both excavation disturbance and seepage pressure. We also analyze the mechanism of unloading and seepage pressure leading to sample failure and construct a fractional creep damage constitutive model that considers the unloading effect. The results include the following findings, firstly, seepage pressure will affect the creep deformation of rock for a long time, and the circumferential expansion of the granite creep process is more obvious than the axial expansion. Secondly, a high seepage pressure will reduce the rock bearing capacity. Under 0, 2 and 4 MPa seepage pressures, the long-term strength of the samples are 193.7 MPa, 177.5 MPa and 162.1 MPa, respectively. Thirdly, the rock damage factor increases with increasing seepage pressure, time and deviatoric stress. Finally, the rationality of a fractional-order model that considers the effect of unloading and seepage is verified by the test data. These research results may provide some reference for the stability analysis of surrounding rock during excavation in environments under high-stress and high-seepage-pressure.
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CHRZANOWSKI, MARCIN y KRZYSZTOF NOWAK. "ON MULTISCALE MODELLING OF CREEP DAMAGE BY MEANS OF CELLULAR AUTOMATA". Journal of Multiscale Modelling 01, n.º 03n04 (julio de 2009): 389–402. http://dx.doi.org/10.1142/s1756973709000153.
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Deterioration of the materials, particularly metals under environmental conditions such as high temperature, alternating loading and chemical aggression is an example of processes which happen on the microstructure levels but project themselves upon macroscopically observed behaviour of materials and structures. This connection between both levels of observation was obvious to many researches, even if they aimed at macroscopic description on the level of continuum mechanics. The wisdom of micro- and macro-coupling was induced by a very complex nature of microstructural processes which demonstrated themselves as transgranular or intergranular failures, just to mention two typical modes of creep failure. The gap between micro- and macro-world was a challenge to both material science and mechanics societies throughout the second half of 20th century. A proposed method to cover this gap for polycrystalline materials is based on Cellular Automata (CA) technique well suited to be used on the microscopic level and giving responses relevant to macroscopic observations. It allows for microstructure modelling to distinguish grains and grain boundaries. Once it is done, a cellular automaton can be attributed to the Representative Volume Element (RVE) and failure mechanism described on the basis of appropriate transition rules. Examples of transgranular and intergranular creep damage growth are demonstrated. This procedure can be extended over the feedback from micro-level to macro-level leading to the formation of so-called CAFE technique.
Tesis sobre el tema "Creep-induced damage mechanism"
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Sun, Yufeng. "Time-dependent hydromechanical behaviour of callovo-oxfordian claystone by anatytical and multiscale numerical methods". Electronic Thesis or Diss., Vaulx-en-Velin, École nationale des travaux publics de l’État, 2023. http://www.theses.fr/2023ENTP0009.
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Dans le contexte du stockage géologique profond des déchets radioactifs, le comportement hydromécanique différé de l’argilite du Callovo-Oxfordien (COx) est étudié afin d’assurer les conditions de sûreté requises pour un stockage à long terme de déchets radioactifs. La première partie de l'étude s'appuie sur une approche phénoménologique menée directement à l'échelle macroscopique du matériaux rocheux et des ouvrages souterrains. Dans un premier temps, un modèle quasi-analytique du comportement hydromécanique d'une cavité sphérique profonde creusée dans un massif rocheux dilatant poro-viscoplastique est présenté. Cette modélisation considère trois étapes d'un cycle de vie simplifié de l’ouvrage souterrain : excavation, convergence libre et comportement post-fermeture. Ensuite, le développement, l’extension et l’évolution de la zone rocheuse endommagée par l'excavation (EDZ, Excavation Damaged Zone) sont étudiés à l'aide d’un code aux éléments finis. Cette zone endommagée fait référence à une région caractérisée par des changements importants et pour la plupart irréversibles des propriétés géochimiques et hydromécaniques de la roche. Des analyses de sensibilité et de probabilité sont aussi effectuées pour étudier l’évolution de l'étendue au cours du temps de l’EDZ. Dans la deuxième partie de l'étude, une approche numérique multi-échelles est utilisée pour étudier les effets de fluage et d'endommagement sur le comportement mécanique. Tout d'abord, un modèle basé sur la micromécanique, dans le cadre de modélisation de type éléments finis au carré (EF²), est développé pour modéliser le comportement à long terme de l'argilite du Callovo-Oxfordien. Pour simuler les effets visqueux de la matrice argileuse, deux mécanismes à l’échelle microscopique ont été introduits : la viscoplasticité des agrégats d'argile et la viscoélasticité de leurs contacts. Ensuite, le modèle de comportement de l’argilite du Callovo-Oxfordien développé à petite échelle est appliqué pour modéliser le comportement de fluage à grande échelle, c’est-à-dire à l'échelle du laboratoire et des galeries souterraines. À partir des résultats de simulations à l'échelle du laboratoire, un processus de fluage en trois étapes est reproduit. Il comprend les étapes de fluage primaire, secondaire et tertiaire. A l’échelle des galeries souterraines, l'effet à long terme de la viscosité est étudié sur l'évolution des convergences des galeries et de l'EDZ. Le drainage à long terme et l’évolution de la pression d’eau interstitielle autour d'une galerie sont aussi étudiés. Enfin, le modèle de fluage à double échelle qui a été développé et utilisé pour simuler le comportement de fluage d'une roche fissurée saturée en eau est étendu au cas partiellement saturé. L’objectif est d’étudier l'interaction hydrique entre la roche autour des galeries souterraines et l'air à l’intérieur de celles-ci qui se produit lorsqu’il y a une circulation d’air humide dans les galeries. Les prédictions du modèle reproduisent la cinétique de drainage et de désaturation des roches saines et endommagéesIn the context of radioactive waste repository, the time-dependent hydromechanical behaviour of the Callovo-Oxfordian (COx) claystone is investigated to ensure the safety conditions required for long-term repository of radioactive wastes.The first two parts of the study are based on the phenomenological approach carried out directly at the macroscale. Firstly, a quasi-analytical model for the hydromechanical behaviour of a deep spherical cavity excavated in a dilatant poro-viscoplastic rock mass is presented, considering three stages of a simplified life cycle: excavation, free convergence and post-closure. Subsequently, the sensitive and probability analyses are carried out using the finite element code Cast3M toinvestigate the time-dependent extent of the Excavation Damaged Zone (EDZ) which refers to a region characterized by significant and mainly irreversible changes in geochemical and hydromechanical properties. In the following, a multiscale numerical approach is employed to investigate its creep and damage behaviour under mechanical condition. Firstly, a micromechanics-based model within the finite element square (FE2) framework is developed to model the short-term and long-term behaviours of saturated COx claystone. For the viscous behaviour, two microscale mechanisms have been introduced: the viscoplasticity of the clay aggregates and the viscoelasticity of their contacts. Then, the creep model of COx claystones developed at small scale is applied to model the large-scale creep behaviour at laboratory and gallery scales. From simulation results of laboratory scale, a clear three-stage creep process is reproduced, including the primary creep stage, second creep stage and tertiary creep stage. At the gallery scale, the long-term effect of viscosity on the gallery convergences, the evolution of EDZ, and the long-term drainage and pore pressure around a gallery are investigated. Finally, the above developed double-scale creep model used to simulate saturated cracked medium is extend to partial saturated case to study the interaction between rock and the atmosphere occurs through air circulation within underground galleries. The emphasis is to study the effect of the gallery air ventilation on hydromechanical behaviour of host rock. The model predictions reproduce the drainage and desaturation kinetics of undisturbed and damaged rock
Capítulos de libros sobre el tema "Creep-induced damage mechanism"
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Zhao, Rong Guo, Wen Bo Luo, Chu Hong Wang y Xin Tang. "Effect of Stress-Induced Damage Evolution on Long-Term Creep Behavior of Nonlinear Viscoelastic Polymer". En Fracture and Damage Mechanics V, 731–34. Stafa: Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/0-87849-413-8.731.
Texto completoActas de conferencias sobre el tema "Creep-induced damage mechanism"
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Islam, Nazrul y Tasnim Hassan. "Damage Evaluation of Grade 91 Thick Cylinder Under Variable Thermal Cyclic Loading Using Continuum Damage Coupled Viscoplastic Models". En ASME 2019 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/pvp2019-93634.
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Abstract This study evaluates creep-fatigue damage in the modified Grade 91 thick-cylinder tested by Japan Atomic Energy Agency (JAEA), to understand the failure mechanism of critical components of Fast Reactor nuclear plants. As modified Grade 91 demonstrated creep-fatigue interaction induced failure mechanisms, finite element analysis of high-temperature components will require a unified constitutive model (UCM) that can simulate various creep-fatigue responses with reasonable accuracy. Hence, a UCM coupled with various advanced modeling features including the continuum damage modeling features is investigated to demonstrate their predictability of the fatigue, creep and creep-fatigue responses of the modified Grade 91 steel. The modified UCM is implemented into ABAQUS for analysis of creep deformation in the thick cylinder benchmark problem. Finite element analysis results are presented to demonstrate how the thermal cycling influences the creep-deformation of this high-temperature component. It is also demonstrated how thermal cycling’s influence on fatigue life can be determined based on the damage variable incorporated in the UCM.
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Dichiaro, Simone, Luca Esposito y Nicola Bonora. "Evaluation of Constraint Effect on Creep Crack Growth by Advanced Creep Modeling and Damage Mechanics". En ASME 2014 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/pvp2014-29105.
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Effects of constraint induced by crack depth and sample geometry on creep crack behavior of high chromium steels was investigated by numerical simulation. An advanced mechanism-based creep model formulation, which accounts for primary and secondary creep stage was used. Here, the transient creep rate is modeled considering the evolution of the internal stress with the activation energy while the steady state creep rate is modelled considering both diffusional and dislocation creep mechanisms. This formulation allows one to predict accurately creep strain accumulation over a wide range of stress and temperature. Model parameters were identified on constant load creep tests and their transferability to the multiaxial state of stress was verified comparing predicted creep life with data obtained on notched bar samples. Continuum damage mechanics was used to predict the occurrence of tertiary creep stage and crack advance. To this purpose, a non-linear damage law, as proposed in Bonora and Esposito [1] was used. The effect of the geometry constrain on creep crack growth was investigated in different sample geometries (C(T), SEN(T), SEN(B), DEN(T) and CCP(T)) for a given crack depth values, and the same biaxiality ratio for SEN(T), SEN(B) and DEN(T). Numerical simulation results were validated by comparison with available experimental data for P91 steels.
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Wu, Xijia y Zhong Zhang. "A Mechanism-Based Approach From Low Cycle Fatigue to Thermomechanical Fatigue Life Prediction". En ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43974.
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Deformation and damage accumulation occur by fundamental dislocation and diffusion mechanisms. An integrated creep-fatigue theory (ICFT) has been developed, based on the physical strain decomposition rule that recognizes the role of each deformation mechanism and thus relate damage accumulation to its underlying physical mechanism(s). The ICFT formulates the overall damage accumulation as a holistic damage process consisting of nucleation and propagation of surface/subsurface cracks in coalescence with internally distributed damage/ discontinuities. These guiding principles run through both isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF) under general conditions. This paper presents a methodology using mechanism-based constitutive equations to describe the cyclic stress strain curve and the non-linear damage accumulation equation incorporating i) rate-independent plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation to predict LCF and TMF lives of ductile cast iron (DCI). The complication of the mechanisms and their interactions in this material provide a good demonstration case for the model, which is in good agreement with the experimental observations.
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Fan, Zhichao, Xuedong Chen, Ling Chen y Jialing Jiang. "Fatigue-Creep Damage Evolution Model and Life Prediction Methods Under Stress Controlled Mode". En ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/creep2007-26151.
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Damage evolution of stress controlled fatigue-creep interaction actually is the ductility exhaustion process induced by cyclic creep and static creep. Based on the ductility dissipation theory and effective stress concept of the continuum damage mechanism (CDM), a new fatigue-creep interaction damage evolution model and life prediction method under stress control mode are proposed, in which mean strain is the damage parameter to define damage variable D, and mean strain rate at half life is the control factor related to fracture lives. As for 1.25Cr0.5Mo steel, stress-controlled fatigue-creep tests with different combination of stress amplitudes and mean stresses at 540°C were conducted to investigate fatigue-creep interaction. The results of damage descriptions indicate that, the damage model and mean strain parameter are applicable to describe damage evolution of cyclic creep-static creep interaction when ductility exhaustion is dominant. The life prediction results are found to be quite satisfactory relative to test data with a ±1.25 error factor, which is much better than that for the Frequency Separation method (FS) and Strain Energy Frequency Modified approach (SEFS). Further more, it is found that, when stress amplitudes are less than mean stresses, drastic interaction between cyclic creep and static creep will accelerate the material damage rate, so that the damage exponent reaches its peak value.
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Payten, Warwick M., David W. Dean y Ken U. Snowden. "Creep-Fatigue Prediction of Low Alloy Ferritic Steels Using a Strain Energy Based Methodology". En ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77208.
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The accumulation of creep-fatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model that calculates the creep damage under conditions of strain control has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material. This then assumes that the creep damage is directly proportional to absorbed internal energy density. The model developed is derived from considerations of mechanistic cavity growth. The model makes use of already existing creep data and relatively easily determined fatigue data for estimation of life under non-steady state conditions. The predictions of the energy-density exhaustion approach are compared with the results of creep-fatigue tests on a low alloy ferritic steel 1/2Cr-1/2Mo-1/4V (CMV) and with creep-fatigue calculations using a number of current models. The predicted results of the energy-density model are found to have good correlation with the measured creep-fatigue lives.
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Sasaki, Yamato, Hiroyuki Itoh, Naokazu Murata, Ken Suzuki y Hideo Miura. "High Temperature Damages of Ni-Base-Superalloy Caused by the Change of Nanotexture Due to Strain-Induced Anisotropic Diffusion". En ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37284.
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In order to assure the reliability of advanced gas turbine systems, it is very important to evaluate the damage of high temperature materials such as Ni-base superalloys under creep and fatigue conditions quantitatively. Since the micro texture of the gamma-prime (γ′) phase was found to vary during the creep damage process, it is possible, therefore, to evaluate the creep damage of this material quantitatively by measuring the change of the micro texture. The mechanism of the directional coarsening of γ′ phases (rafting) of Ni-base superalloy under an uni-axial strain at high temperatures was analyzed by molecular dynamics (MD) analysis. The stress-induced anisotropic diffusion of Al atoms perpendicular to the initially finely dispersed γ/γ′ interface in the superalloy crystal was observed clearly in a Ni(001)/Ni3Al(001) interface structure. The stress-induced anisotropic diffusion was validated by experiment using the stacked thin films structures which consisted of the (001) face-centered cubic (FCC) interface. The reduction of the diffusion of Al atoms perpendicular to the interface is thus, effective for improving the creep and fatigue resistance of the alloy. It was also found by MD analysis that the dopant elements in the superalloy also affected the strain-induced diffusion of Al atoms. Palladium was one of the most effective elements which restrain Al atoms from moving around the interface under the applied stress.
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Miura, Hideo, Ken Suzuki, Yamato Sasaki, Tomohiro Sano y Naokazu Murata. "High Temperature Damage of Ni-Base Superalloy Caused by the Change of Microtexture due to the Strain-Induced Anisotropic Diffusion of Component Elements". En ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-62411.
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In order to assure the reliability of advanced gas turbine systems, it is very important to evaluate the damage of high temperature materials such as Ni-base superalloys under creep and fatigue conditions quantitatively. Since the micro texture of the gamma-prime (γ′) phase was found to vary during the creep damage process, it is possible, therefore, to evaluate the creep damage of this material quantitatively by measuring the change of the micro texture. The mechanism of the directional coarsening of γ′ phasesof Ni-base superalloy under uni-axial strain at high temperatures, which is called rafting, was analyzed by using molecular dynamics (MD) analysis. The stress-induced anisotropic diffusion of Al atoms perpendicular to the finely dispersed γ/γ′ interface in the superalloy was observed clearly in a Ni(001)/Ni3Al(001) interface structure. The stress-induced anisotropic diffusion was validated by experiment using the stacked thin films structures which consisted of the (001) face-centered cubic (FCC) interface. The reduction of the diffusion of Al atoms perpendicular to the interface is thus, effective for improving the creep and fatigue resistance of the alloy. It was also found by MD analysis that the dopant elements in the superalloy also affected the strain-induced diffusion of Al atoms. Both palladium and tantalum were effective elements which restrain Al atoms from moving around the interface under the applied stress, while titanium and tungsten accelerated the strain-induced anisotropic diffusion, and thus, the rafting phenomenon.
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Tan, Jian-Ping, Guo-Zhen Wang, Fu-Zhen Xuan, Shan-Tung Tu y Zheng-Dong Wang. "Effect of the Out-of-Plane Constraint on Creep Crack Growth Property of Cr-Mo-V Type Steel". En ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57300.
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In order to establish an accurate integrity assessment of structures containing defects at high temperature, it is necessary to clarify the constraint effect on creep crack growth (CCG) property. However, the effect of the out-of-plane creep constraint induced by the specimen thicknesses has been little studied. In this study, the CCG properties and fracture mechanism of Cr-Mo-V type steel at 566°C were investigated by using the compact tension specimens with different thicknesses. The results show that the data of the CCG rate da/dt versus C* lie within a relatively tight scatter band on log-log scale for the specimens with different thicknesses at higher values of C*. In addition, the differences of CCG rate becomes large with C* decreasing. It means that the effect of out-of-plane constraint on CCG rate is dependent on the load level (C*). The reason for the similar CCG rate is that the creep damage and fracture mechanism of void growth at grain boundary ahead of crack tips in the specimens with different thicknesses does not essentially change. The size rc of the creep damage and fracture process zone in front of crack tips is related to the specimen thickness, and the damage rate fields over the process zone are similar for the specimens with different thicknesses. The deformation near the crack tip obscures the constraint effect. Based on a reference stress field under plane strain state and the creep process zone rc, in-plane and out-of-plane constraint parameter Rd and Td were defined and the creep crack-tip constraint effect induced by specimen thickness were quantitatively examined. The factors of creep time and load level (C*) influencing the constraint effect were analyzed.
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Suzuki, Ken, Tomohiro Sano y Hideo Miura. "Effect of Alloying Elements on Creep and Fatigue Damage of Ni-Base Superalloy Caused by Strain-Induced Anisotropic Diffusion". En ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-64314.
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In order to make clear the mechanism of the directional coarsening (rafting) of γ′ phases in Ni-base superalloys under uni-axial tensile strain, molecular dynamics (MD) analysis was applied to investigate effects of alloying elements on diffusion characteristics around the interface between the γ phase and the γ′ phase. In this study, a simple interface structure model corresponding to the γ/γ′ interface, which consisted of Ni as γ and Ni3Al as γ′ structure, was used to analyze the diffusion properties of Ni and Al atoms under tensile strain. The strain-induced anisotropic diffusion of Al atoms perpendicular to the interface between the Ni(001) layer and the Ni3Al(001) layer was observed in the MD simulation, suggesting that the strain-induced anisotropic diffusion of Al atoms in γ′ phase is one of the dominant factors of the kinetics of the rafting during creep damage. The effect of alloying elements in the Ni-base superalloy on the strain-induced anisotropic diffusion of Al atoms was also analyzed. Both the atomic radius and the binding energy with Al and Ni of the alloying element are the dominant factors that change the strain-induced diffusion of Al atoms in the Ni-base super-alloy.
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Luo, Yifan, Shogo Tezuka, Koki Nakayama, Ayumi Nakayama, Ken Suzuki y Hideo Miura. "Creep-Fatigue Damage of Heat-Resistant Alloys Caused by the Local Lattice Mismatch-Induced Acceleration of the Generation and Accumulation of Dislocations and Vacancies". En ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-68489.
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Abstract Degradation mechanism of the strength of a grain boundary in Ni-base superalloy under creep-fatigue loading at elevated temperature was investigated by using the modified Arrhenius equation, which explained the stress-induced acceleration of the local generation and diffusion of dislocations and vacancies. EBSD analysis confirmed that dislocations and vacancies started to generate and accumulate around grain boundaries and the interface between precipitates and matrix in grains. The generation and accumulation were accelerated around the interfaces with large difference in the lattice constant between the nearby crystallographic phases and grains. The activation energies of the diffusion of dislocations and vacancies measured under the harsh condition was much lower than those measured under the thermodynamically stable conditions. It was confirmed that there are two main acceleration mechanisms of the degradation of the crystallinity and strength of grain boundaries under a tensile stress at elevated temperatures: the acceleration of the generation and diffusion of dislocations and the acceleration of accumulation of voids due to the outward diffusion of component atoms from the grain boundaries. These phenomena were explained by the modified Arrhenius equations in which the effective activation energies were changed by the summation of the applied nominal stress and the localized internal stress around various interfaces quantitatively.