Articles de revues : « Environment-assisted fatigue »

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Wu, X. J., et W. Wallace. « On low-temperature environment-assisted fatigue crack propagation ». Metallurgical and Materials Transactions A 25, n^o 3 (mars 1994) : 658–59. http://dx.doi.org/10.1007/bf02651611.

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Sandviknes, J. S. S., N. D. Adasooriya, D. Pavlou et T. Hemmingsen. « Environment-assisted fatigue of steel bridges : A conceptual framework for life assessment ». IOP Conference Series : Materials Science and Engineering 1201, n^o 1 (1 novembre 2021) : 012045. http://dx.doi.org/10.1088/1757-899x/1201/1/012045.

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Abstract This paper presents a framework based on a recently proposed fatigue strength curve of corroded steel to assess the life of an existing steel bridge exposed to environment-assisted fatigue. Environment-assisted cracking (EAC) and how it affects the structural integrity of steel bridges are introduced by the framework. Determination of both corroded and uncorroded details in a corrosive environment are also included in this framework. To conform the applicability and significance, a fatigue life of a railway bridge was assessed by methods given in the framework. The obtained fatigue lives were compared. The difference of the estimated fatigue lives emphasizes the importance of having this framework to consider the interaction of corrosion and fatigue mechanisms.

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Zelizko, V., A. Grossmuller et M. V. Swain. « Environment Assisted Fatigue Crack Growth Behaviour of Mg-PSZ ». Materials Science Forum 34-36 (janvier 1991) : 201–5. http://dx.doi.org/10.4028/www.scientific.net/msf.34-36.201.

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Shen, R., Y. B. He et M. Cao. « Research on the Environment Assisted Fatigue Based on Flaw Tolerance Method ». Procedia Engineering 130 (2015) : 1580–91. http://dx.doi.org/10.1016/j.proeng.2015.12.329.

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Gu, Kyoung Hee, Ki Sik Lee, Gum Hwa Lee et Ki Woo Nam. « Evaluation of Fatigue Life of Ultra-High-Strength Steel under Stress Corrosion Environment ». Applied Mechanics and Materials 907 (22 juin 2022) : 1–7. http://dx.doi.org/10.4028/p-s303xf.

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Ultra-high-strength steel (UHSS) structures are exposed to corrosive environments during service, and hydrogen-assisted cracking (HAC) may occur owing to stress corrosion cracking and hydrogen embrittlement. In this study, the HAC threshold stress intensity factor and fatigue life of UHSS steel were evaluated by applying stress in a corrosive environment to prevent structural fracture. For specimen with semicircular slits by electric discharge machining, fatigue limit was obtained by static fatigue test under corrosive environment. The fatigue limit of the crack specimen was evaluated by the fatigue limit of the experiment and HAC threshold stress intensity factor, and comparative evaluation was performed. On the surface of cracks, grain boundaries were embrittled by corrosion, and grains were clearly observed. Meanwhile, cracks in the surface direction propagated slightly, unlike cracks in the depth direction. The static fatigue limit of UHSS (SKD11:HV670) was determined to be 400 MPa, and the fatigue limit of the crack specimen could be evaluated. The experimental results agreed well with the evaluation results.

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Bruchhausen, Matthias, Gintautas Dundulis, Alec McLennan, Sergio Arrieta, Tim Austin, Román Cicero, Walter-John Chitty et al. « Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions ». Metals 11, n^o 2 (10 février 2021) : 307. http://dx.doi.org/10.3390/met11020307.

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A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

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Chen, Xingyang, Linlin Ma, Haoping Xie, Fengting Zhao, Yufeng Ye et Lin Zhang. « Effects of external hydrogen on hydrogen-assisted crack initiation in type 304 stainless steel ». Anti-Corrosion Methods and Materials 67, n^o 3 (27 avril 2020) : 331–35. http://dx.doi.org/10.1108/acmm-02-2020-2258.

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Purpose The purpose of this paper is to present a crack initiation mechanism of the external hydrogen effect on type 304 stainless steel, as well as on fatigue crack propagation in the presence of hydrogen gas. Design/methodology/approach The effects of external hydrogen on hydrogen-assisted crack initiation in type 304 stainless steel were discussed by performing fatigue crack growth rate and fatigue life tests in 5 MPa argon and hydrogen. Findings Hydrogen can reduce the incubation period of fatigue crack initiation of smooth fatigue specimens and greatly promote the fatigue crack growth rate during the subsequent fatigue cycle. During the fatigue cycle, hydrogen invades into matrix through the intrusion and extrusion and segregates at the boundaries of α′ martensite and austenite. As the fatigue cycle increased, hydrogen-induced cracks would initiate along the slip bands. The crack initiation progress would greatly accelerate in the presence of hydrogen. Originality/value To the best of the authors’ knowledge, this paper is an original work carried out by the authors on the hydrogen environment embrittlement of type 304 stainless steel. The effects of external hydrogen and argon were compared to provide understanding on the hydrogen-assisted crack initiation behaviors during cycle loading.

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FUKUTA, Yuichi, Hiroshi KANASAKI, Seiji ASADA et Toshiya SARUWATARI. « OS0803 Refinement of Strain Rate that Shows No Environment Assisted Fatigue for Austenitic Stainless Steels in PWR Environment ». Proceedings of the Materials and Mechanics Conference 2012 (2012) : _OS0803–1_—_OS0803–3_. http://dx.doi.org/10.1299/jsmemm.2012._os0803-1_.

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Octavia, Johanna Renny, Peter Feys et Karin Coninx. « Development of Activity-Related Muscle Fatigue during Robot-Mediated Upper Limb Rehabilitation Training in Persons with Multiple Sclerosis : A Pilot Trial ». Multiple Sclerosis International 2015 (2015) : 1–11. http://dx.doi.org/10.1155/2015/650431.

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Robot-assisted rehabilitation facilitates high-intensity training of the impaired upper limb in neurological rehabilitation. It has been clinically observed that persons with Multiple Sclerosis (MS) have difficulties in sustaining the training intensity during a session due to the development of activity-related muscle fatigue. An experimental observational pilot study was conducted to examine whether or not the muscle fatigue develops in MS patients during one session of robot-assisted training within a virtual learning environment. Six MS patients with upper limb impairment (motricity index ranging from 50 to 91/100) and six healthy persons completed five training bouts of three minutes each performing lifting tasks, while EMG signals of anterior deltoid and lower trapezius muscles were measured and their subjective perceptions on muscle fatigue were registered. Decreased performance and higher subjective fatigue perception were present in the MS group. Increased mean EMG amplitudes and subjective perception levels on muscle fatigue were observed in both groups. Muscle fatigue development during 15′ training has been demonstrated in the arm of MS patients, which influences the sustainability of training intensity in MS patients. To optimize the training performance, adaptivity based on the detection of MS patient’s muscle fatigue could be provided by means of training program adjustment.

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Poulain, Thibault, Laurent de Baglion, Jose Mendez et Gilbert Hénaff. « Influence of Strain Rate and Waveshape on Environmentally-Assisted Cracking during Low-Cycle Fatigue of a 304L Austenitic Stainless Steel in a PWR Water Environment ». Metals 9, n^o 2 (8 février 2019) : 197. http://dx.doi.org/10.3390/met9020197.

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In this paper, the low cycle fatigue resistance of a 304L austenitic stainless steel in a simulated pressurized water reactor (PWR) primary water environment has been investigated by paying a special attention to the interplay between environmentally-assisted cracking mechanisms, strain rate, and loading waveshape. More precisely, one of the prime interests of this research work is related to the consideration of complex waveshape signals that are more representative of solicitations encountered by real components. A detailed analysis of stress-strain relation, surface damage, and crack growth provides a preliminary ranking of the severity of complex, variable strain rate signals with respect to triangular, constant strain-rate signals associated with environmental effects in air or in PWR water. Furthermore, as the fatigue lives in PWR water environment are mainly controlled by crack propagation, the crack growth rates derived from striation spacing measurement and estimated from interrupted tests have been carefully examined and analyzed using the strain intensity factor range ΔKε. It is confirmed that the most severe signal with regards to fatigue life also induces the highest crack growth enhancement. Additionally two characteristic parameters, namely a threshold strain εth* and a time T*, corresponding to the duration of the effective exposure of the open cracks to PWR environment have been introduced. It is shown that the T* parameter properly accounts for the differences in environmentally-assisted growth rates as a function of waveshape.

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Xing, X. Q., J. N. Lu, J. W. Jian, L. J. Li et Z. C. Luo. « Effect of environment-assisted cracking on the premature fatigue failure of high-strength valve springs ». Engineering Failure Analysis 126 (août 2021) : 105466. http://dx.doi.org/10.1016/j.engfailanal.2021.105466.

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Cabrini, Marina, Sergio Lorenzi, Tommaso Pastore et Fabio Maria Bolzoni. « Environmentally assisted cracking of pipeline steels in CO2 containing environment at near-neutral pH ». Corrosion Reviews 35, n^o 4-5 (26 octobre 2017) : 309–23. http://dx.doi.org/10.1515/corrrev-2017-0053.

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AbstractThe paper summarizes the results obtained by authors concerning near-neutral stress corrosion cracking (SCC) phenomena on buried pipelines. Stress corrosion tests according to different methodologies and fatigue propagation tests were executed on traditional steel grades. Tests were performed also on specimens pre-corroded according to a procedure developed to produce localized attacks similar to those observed during failure analysis on pipelines, acting as preferential sites for crack nucleation. Electrochemical tests were carried out in order to evaluate the influence of environmental parameter on pit formation. The main role of continuous plastic deformations on near-neutral SCC is confirmed. The effect of pH, CO2, and bicarbonate concentrations on pitting formation is discussed.

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Kasul, David B., et Lloyd A. Heldt. « Environmental Effects on the Cracking of Engineering Materials ». MRS Bulletin 14, n^o 8 (août 1989) : 37–43. http://dx.doi.org/10.1557/s0883769400061947.

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A material's susceptibility to cracking may be significantly affected by its chemical environment. Stress corrosion cracking (SCC), liquid metal embrittle-ment (LME), hydrogen embrittlement (HE), and corrosion fatigue are examples of environmental effects which cause ductility or endurance losses through environment-assisted cracking (EAC). Under certain conditions, virtually all commercially important materials are susceptible to one or more of the above embrittlement processes. Cracking may occur intergranularly, transgranularly, or in a mixed mode, depending on conditions. Much is known about the metallurgical and environmental conditions which promote environment-assisted cracking, and prudent control of these is often successful in mitigating or preventing cracking. However, in spite of our understanding of the factors controlling SCC, LME, and HE, the responsible mechanisms remain elusive.This article will (1) review some of the important variables affecting these phenomena, such as stress, stress intensity, material microstructure, strain rate, electrochemical potential and pH, and (2) attempt to relate phenomeno-logical characteristics of environment-induced embrittlement to several mechanisms proposed for environment-assisted cracking, as they are understood today.The problem of stress corrosion cracking is unquestionably the most costly of environmental cracking phenomena, with losses occurring in a wide variety of service environments. Liquid metal embrittlement is of concern in nuclear power and other industries. Hydrogen embrittlement, first recognized as an embrittler of iron in 1873, causes cracking problems in applications ranging from welding to oil drilling. In all, the list of situations in which environment-assisted cracking occurs is long and is likely to grow as materials are increasingly challenged by the severity of their service conditions.

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Krausz, Alexander S., et Klara Krausz. « The Fracture Kinetics of Subcritical Environment Assisted Fatigue Crack Propagation Processes / Die Bruchkinetik subkritischer, umgebungsunterstützter Ermüdungsrißausbreitung ». International Journal of Materials Research 81, n^o 3 (1 mars 1990) : 181–92. http://dx.doi.org/10.1515/ijmr-1990-810304.

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Krausz, K., X. Wu, Z. Lian et A. S. Krausz. « On the Constitutive Law of Environment Assisted Fatigue : The Physical Meaning ofthe Paris Type’Eguatiöns Part 1 ». International Journal of Materials Research 83, n^o 4 (1 avril 1992) : 283–88. http://dx.doi.org/10.1515/ijmr-1992-830414.

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Gnanasekaran, Balachander, Jie Song, Vijay Vasudevan et Yao Fu. « Corrosion Fatigue Characteristics of 316L Stainless Steel Fabricated by Laser Powder Bed Fusion ». Metals 11, n^o 7 (29 juin 2021) : 1046. http://dx.doi.org/10.3390/met11071046.

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Laser powder bed fusion (LPBF) has been increasingly used in the fabrication of dense metallic structures. However, the corrosion related properties of LPBF alloys, in particular environment-assisted cracking, such as corrosion fatigue properties, are not well understood. In this study, the corrosion and corrosion fatigue characteristics of LPBF 316L stainless steels (SS) in 3.5 wt.% NaCl solution have been investigated using an electrochemical method, high cycle fatigue, and fatigue crack propagation testing. The LPBF 316L SSs demonstrated significantly improved corrosion properties compared to conventionally manufactured 316L, as reflected by the increased pitting and repassivation potentials, as well as retarded crack initiation. However, the printing parameters did not strongly affect the pitting potentials. LPBF samples also demonstrated enhanced capabilities of repassivation during the fatigue crack propagation. The unique microstructural features introduced during the printing process are discussed. The improved corrosion and corrosion fatigue properties are attributed to the presence of columnar/cellular subgrains formed by dislocation networks that serve as high diffusion paths to transport anti-corrosion elements.

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Stanzl-Tschegg, Stefanie E. « When do small fatigue cracks propagate and when are they arrested ? » Corrosion Reviews 37, n^o 5 (25 septembre 2019) : 397–418. http://dx.doi.org/10.1515/corrrev-2019-0023.

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AbstractThe formation of small and long cracks and their propagation or arrest are treated drawing special attention to the (a) impact of environment and (b) several loading parameters (R-ratio, stress/strain-amplitude, constant-amplitude and variable-amplitude loading, superimposed loading, ultrasonic fatigue loading, and frequency effects) for three groups of metallic materials (two high-strength steels, 7075 and 2024 Al alloys, polycrystalline copper). The influence of these parameters on lifetimes and fatigue crack propagation behavior being determined by microstructural features on all levels of magnification (ranging from several millimeters to nanometers) is presented. A review of the state of knowledge according to literature is given in the introduction. The following results were obtained, and models for their interpretation were presented: The development (growth or arrest) of small cracks into a long crack is driven by several competing processes (due to material, way of loading, environment, etc.). The environment plays a predominant role. Especially in the high-cycle and very-high cycle regime, the complexity of interacting processes needs further – mainly experimental – investigations. Some further studies relate to different loading conditions and possibilities of testing considering newly developed material. Experiments in high vacuum have to form the basis for studying environmentally assisted fatigue response.

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GAO, ZHIWEI, DONGPO WANG, BAOMING GONG, CAIYAN DENG, SHAOJIE WU et HAI ZHANG. « VHCF Behavior of Welded Joints with HFMI Treatment under Moisture Conditions ». Welding Journal 101, n^o 1 (1 janvier 2022) : 27–42. http://dx.doi.org/10.29391/2022.101.003.

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Fatigue tests of cruciform welded joints made of Q355B steel at very-high-cycle fatigue (VHCF) regimes were carried out on as-welded specimens using highfrequency mechanical impact (HFMI) treatment in dry air and water-spray environments, respectively. The influence of the environment on fatigue life was more obvious in the VHCF regime. It was found that S-N curves became flat over the range of 106–108 cycles for as-welded specimens, while a continuously decreasing S-N curve existed for HFMI-treated specimens. Fatigue cracks initiated from the weld toe of the as-welded specimens in dry air and water-spray environments. Due to residual stress, the crack initiation site transition of HFMI-treated specimens from the weld toe to the weld root and base metal was observed at lower stress levels. Moreover, hydrogen-assisted quasi-cleavage and intergranular fracture were captured using a scanning electron microscope and a hydrogen permeation test.

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Pinto-Bernal, Maria J., Carlos A. Cifuentes, Oscar Perdomo, Monica Rincón-Roncancio et Marcela Múnera. « A Data-Driven Approach to Physical Fatigue Management Using Wearable Sensors to Classify Four Diagnostic Fatigue States ». Sensors 21, n^o 19 (25 septembre 2021) : 6401. http://dx.doi.org/10.3390/s21196401.

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Physical exercise contributes to the success of rehabilitation programs and rehabilitation processes assisted through social robots. However, the amount and intensity of exercise needed to obtain positive results are unknown. Several considerations must be kept in mind for its implementation in rehabilitation, as monitoring of patients’ intensity, which is essential to avoid extreme fatigue conditions, may cause physical and physiological complications. The use of machine learning models has been implemented in fatigue management, but is limited in practice due to the lack of understanding of how an individual’s performance deteriorates with fatigue; this can vary based on physical exercise, environment, and the individual’s characteristics. As a first step, this paper lays the foundation for a data analytic approach to managing fatigue in walking tasks. The proposed framework establishes the criteria for a feature and machine learning algorithm selection for fatigue management, classifying four fatigue diagnoses states. Based on the proposed framework and the classifier implemented, the random forest model presented the best performance with an average accuracy of ≥98% and F-score of ≥93%. This model was comprised of ≤16 features. In addition, the prediction performance was analyzed by limiting the sensors used from four IMUs to two or even one IMU with an overall performance of ≥88%.

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Voss, M. Lauren, J. Paige Pope et Jennifer L. Copeland. « Reducing Sedentary Time among Older Adults in Assisted Living : Perceptions, Barriers, and Motivators ». International Journal of Environmental Research and Public Health 17, n^o 3 (22 janvier 2020) : 717. http://dx.doi.org/10.3390/ijerph17030717.

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Older adults accumulate more sedentary time (ST) than any other age group, especially those in assisted living residences (ALRs). Reducing prolonged ST could help maintain function among older adults. However, to develop effective intervention strategies, it is important to understand the factors that influence sedentary behavior. The purpose of this study was to explore perceptions of ST as well as barriers and motivators to reducing ST among older adults in assisted living, in the context of the Social Ecological Model (SEM). Using a qualitative description approach, we sought to learn about participants’ perceptions of sedentary time in their daily lives. Semi-structured focus groups were held at six ALRs with 31 participants (84% women, 83.5 ± 6.5 years). Data were transcribed and coded using an inductive thematic approach. Themes were categorized based on four levels of the SEM: individual, social, physical environment, and organization. Many reported barriers were at the individual level (e.g., lack of motivation, pain, fatigue) while others were associated with the organization or social environment (e.g., safety concerns, lack of activities outside of business hours, and social norms). These findings suggest that there are unique challenges and opportunities to consider when designing ST interventions for assisted living.

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Pañeda, Emilio Martínez. « Progress and opportunities in modelling environmentally assisted cracking ». RILEM Technical Letters 6 (19 juillet 2021) : 70–77. http://dx.doi.org/10.21809/rilemtechlett.2021.145.

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Environmentally assisted cracking phenomena are widespread across the transport, defence, energy and construction sectors. However, predicting environmentally assisted fractures is a highly cross-disciplinary endeavour that requires resolving the multiple material-environment interactions taking place. In this manuscript, an overview is given of recent breakthroughs in the modelling of environmentally assisted cracking. The focus is on the opportunities created by two recent developments: phase field and multi-physics modelling. The possibilities enabled by the confluence of phase field methods and electro-chemo-mechanics modelling are discussed in the context of three environmental assisted cracking phenomena of particular engineering interest: hydrogen embrittlement, localised corrosion and corrosion fatigue. Mechanical processes such as deformation and fracture can be coupled with chemical phenomena like local reactions, ionic transport and hydrogen uptake and diffusion. Moreover, these can be combined with the prediction of an evolving interface, such as a growing pit or a crack, as dictated by a phase field variable that evolves based on thermodynamics and local kinetics. Suitable for both microstructural and continuum length scales, this new generation of simulation-based, multi-physics phase field models can open new modelling horizons and enable Virtual Testing in harmful environments.

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Kim, Ho-Sub, Hyeon Bae Lee, Junjie Chen, Changheui Jang, Tae Soon Kim, Gary L. Stevens et Kawaljit Ahluwalia. « Effect of zinc on the environmentally-assisted fatigue behavior of 316 stainless steels in simulated PWR primary environment ». Corrosion Science 151 (mai 2019) : 97–107. http://dx.doi.org/10.1016/j.corsci.2019.02.012.

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Underwood, John H., et Edward Troiano. « Critical Fracture Processes in Army Cannons : A Review ». Journal of Pressure Vessel Technology 125, n^o 3 (1 août 2003) : 287–92. http://dx.doi.org/10.1115/1.1593075.

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Fast fracture in cannons can be well described using elastic-plastic fracture toughness, in combination with comparisons of cannon section size relative to the size required to maintain plane strain fracture. Fatigue fracture of cannon tubes is modeled from results of full-size fatigue tests that simulate cannon firing. These tests are also the basis of fatigue-intensity-factor modeling of fatigue life, which incorporates material strength, initial crack size and Bauschinger-modified autofrettage residual stress into life predictions. Environment-assisted fracture in the thermally damaged near-bore region of fired cannons is shown to be controlled by hydrogen. High strength cannon steels are susceptible to hydrogen; cannon propellant gases provide the hydrogen; and the source of sustained tensile stress is the near-bore thermal damage and compressive yielding. A thermo-mechanical model predicts tensile residual stress of similar depth to that of observed hydrogen cracks. Coating fracture in the thermal-damage region of fired cannons is characterized and modeled. The Evans/Hutchinson slip zone concept is extended to calculate in-situ coating fracture strength from observed crack spacing and hardness in the damaged region.

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BERGNER, F., H. BERSCH, H. WORCH et G. ZOUHAR. « Mapping of the rate-controlling steps for environment-assisted fatigue crack growth applied to the aluminium alloy 6013 T6 ». International Journal of Fatigue 24, n^o 8 (août 2002) : 831–39. http://dx.doi.org/10.1016/s0142-1123(02)00002-6.

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James, L. A., T. A. Auten, T. J. Poskie et W. H. Cullen. « Corrosion Fatigue Crack Growth in Clad Low-Alloy Steels—Part I : Medium-Sulfur Forging Steel ». Journal of Pressure Vessel Technology 119, n^o 3 (1 août 1997) : 249–54. http://dx.doi.org/10.1115/1.2842301.

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Corrosion fatigue crack propagation tests were conducted on a medium-sulfur ASTM A508-2 forging steel overlaid with weld-deposited alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 30.3–38.3 mm, and depths of 13.1–16.8 mm. The experiments were conducted in a quasi-stagnant low-oxygen (O2 < 10ppb) aqueous environment at 243°C, under loading conditions (ΔK, R, and cyclic frequency) conducive to environmentally assisted cracking (EAC) in higher-sulfur steels under quasi-stagnant conditions. Earlier experiments on unclad compact tension specimens of this heat of steel did not exhibit EAC, and the present experiments on semi-elliptical surface cracks penetrating cladding also did not exhibit EAC.

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Kariya, K., Norio Kawagoishi, H. Maeda, Q. Chen, Masahiro Goto et Yan Nu. « Fatigue Fracture Mechanism of Extruded Al Alloy 7075-T6 in High Humidity ». Key Engineering Materials 488-489 (septembre 2011) : 45–48. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.45.

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Effect of high humidity on growth mechanism of a fatigue crack was investigated for an extruded bar of an age-hardened Al alloy 7075-T6 which had the marked texture of plane (111). Fracture in high humidity occurred by the growth of a shear mode crack under high stress levels, though a crack propagated in a tensile mode under low stress ones, macroscopically. Many voids and slip planes were observed on the fracture surface yielded by the shear mode crack. Especially most of the fracture surface was occupied by voids where the crack was small. The void percentage decreased with increasing in the crack depth. Fracture surface yielded by the shear mode crack was a plane (100). The growth direction of the shear mode crack to the cross section of specimen was about 55° corresponding to the angle composed by this plane and the texture of plane (111). These results suggest that the shear mode crack was related to microstructure, stress and environment. The growth mechanism of the shear mode crack assisted by hydrogen was proposed based on the results of the acceleration of crack growth and the formation of voids in high humidity.

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Kishlakov, Daniel L., Pavel V. Tarakanov, Georgy V. Shashurin et Yury V. Berchun. « Hydrogen Aggressive Media Impact on Cycling Durability of Structure Components ». Materials Science Forum 844 (mars 2016) : 27–30. http://dx.doi.org/10.4028/www.scientific.net/msf.844.27.

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To develop modern CAE systems for durable and reliable structure components design, mathematical modeling of environmentally assisted metal cracking becomes very important. For structure components exploited in aggressive environment and under cyclic load, it is a problem of today. Besides, mathematical rule of damage accumulation of different causes (for instance, hydrogen media impact and cycling) is rarely used in CAE systems, but if such rule was used, crack propagation simulation considering several damage causes would be possible.Environmentally assisted metal cracking model (developed earlier by authors) is described in the paper. This model considers cyclic load and hydrogen embrittlement, the most important characteristics of which are hydrogen environmental concentration and load frequency respectively.The authors’ model successfully predicts effect, known from certain experimental data, that the greater is the frequency, the less hydrogen embrittlement affects fatigue cracks propagation and, vice-versa, that there are certain boundaries of cycling frequency for which embrittlement effect is comparably big.Such boundaries of frequency were numerically estimated by means of the presented model. Plots showing dependency of the component’s life on different defect and loading features are shown.

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Saxena, Ashok, et Kevin Nibur. « Fatigue Crack Growth Behaviour of High Strength Ferritic Steels in High Pressure Hydrogen ». MATEC Web of Conferences 165 (2018) : 03008. http://dx.doi.org/10.1051/matecconf/201816503008.

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The design of safe and low-cost, high-pressure hydrogen storage systems are a critical need for harnessing clean power but must consider the propensity of hydrogen to accelerate fatigue crack growth rates in the construction materials. Design of safe pressure vessels needs robust models for predicting crack growth rates and how they are affected by variables such as loading frequency, load ratios, hydrogen pressure, gaseous impurities, temperature, and material variability. In this study, fatigue crack growth rates were measured in the liner material in 10 MPa gaseous hydrogen at various load ratios, R, in the range -1 ≤ R ≤ 0.2. The effects of varying loading frequency were investigated, and the results were pooled with those from literature for similar alloys tested in 103 MPa gaseous hydrogen pressure. The differences in crack growth rates between H2 pressures of 10 to 103 MPa as well as the effects of frequency on the environment assisted crack growth rates were assessed. Loading frequency effects tend to saturate at frequencies of 1 Hz and less. H2 pressure effects appear to saturate at pressures of 45MPa, while load ratio effects are not significant for –1 ≤ R ≤ 0.2 but become important for R ≥ 0.2.

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Öcal, Mustafa, et Recep Sadeler. « Corrosion fatigue behavior of Al-5Mg coated AISI 316L stainless steel in sodium chloride environments under bending load ». Anti-Corrosion Methods and Materials 66, n^o 1 (7 janvier 2019) : 34–39. http://dx.doi.org/10.1108/acmm-04-2018-1924.

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Purpose The purpose of this study is to describe the environmentally assisted cracking (EAC) of AISI 316L stainless steel as bare and coated cases in several corrosion environments. The main purpose of this study is to extend the lifespan of 316L material under corrosive fatigue in sodium chloride environments. Design/methodology/approach Fatigue tests carried out by using a Schenk type plane bending fatigue machine made by Tokyokoki Co. A scanning electron microscope (SEM) was used to observe the fracture surfaces and tested specimen surfaces. The micro-Vickers hardness of specimens was measured by using a PC-controlled Buehler–Omnimet tester. Findings Under reciprocating bending condition (R = −1) the behavior of 316L SS bare samples and 316L SS coated with Al-5%Mg samples were investigated comparatively at room temperature in ambient air and in several corrosion solutions. The results obtained from the data showed that Al-5Mg coating procedure significantly stabilized the 316L SS even in the most aggressive environment 5 per cent NaCl solution as compared with bare samples. Originality/value Al-5Mg coating showed a stable structure under the corrosion liquids used in the experiments. The coating material served as a stable barrier between the base material and the corrosion fluid, thus ensuring a tightness even in long-term tests below the endurance limit.

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Ogawa, Yuhei, Domas Birenis, Hisao Matsunaga, Osamu Takakuwa, Junichiro Yamabe, Øystein Prytz et Annett Thøgersen. « Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part I : Intergranular crack propagation at relatively low stress intensities ». MATEC Web of Conferences 165 (2018) : 03011. http://dx.doi.org/10.1051/matecconf/201816503011.

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The role of hydrogen on intergranular (IG) fracture in hydrogen-assisted fatigue crack growth (HAFCG) of a pure iron at low stress intensity was discussed in terms of the microscopic deformation structures near crack propagation paths. The main cause of IG fracture was assumed to be the hydrogen-enhanced dislocation structure evolution and subsequent microvoids formation along the grain boundaries. Additionally, the impact of such IG cracking on the macroscopic FCG rate was evaluated according to the dependency of IG fracture propensity on the hydrogen gas pressure. It was first demonstrated that the increased hydrogen pressure results in the larger area fraction of IG and corresponding faster FCG rate. Moreover, gaseous hydrogen environment also had a positive influence on the FCG rate due to the absence of oxygen and water vapor. The macroscopic crack propagation rate was controlled by the competition process of said positive and negative effects.

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Takakuwa, Osamu, Yuhei Ogawa, Saburo Okazaki, Masami Nakamura et Hisao Matsunaga. « A mechanism behind hydrogen-assisted fatigue crack growth in ferrite-pearlite steel focusing on its behavior in gaseous environment at elevated temperature ». Corrosion Science 168 (mai 2020) : 108558. http://dx.doi.org/10.1016/j.corsci.2020.108558.

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Hall, Meryl M. « Effect of cyclic frequency on fracture mode transitions during corrosion fatigue cracking of an Al-Zn-Mg-Cu alloy ». Corrosion Reviews 33, n^o 6 (1 novembre 2015) : 315–34. http://dx.doi.org/10.1515/corrrev-2015-0045.

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AbstractThere are complex issues remaining to be resolved before environment-assisted cracking models can be included in structural mechanics programs that are currently used to analyze mechanical fatigue crack growth. Considered here is the effect of cyclic frequency on fracture mode transitions that occur during corrosion fatigue of high-strength Al-Zn-Mg-Cu alloys. These alloys are used in civilian and military aircraft applications where they are exposed to detrimental aqueous saline environments. A previously developed “critical hydrogen at a critical distance” crack growth model is used to rationalize the observed transitions in crack-path fracture-modes, from intergranular (IG), to brittle transgranular (BTG), to ductile transgranular (DTG), as the alternating stress intensity factor and cyclic frequency increase beyond critical values. Corrosion fatigue crack growth rate data obtained on Al-Zn-Mg-Cu alloy 7017-T651 base metal and heat-affected “white zone” metal tested in aqueous NaCl solutions over a frequency range of 0.01–70 Hz are analyzed. For the white zone metal, dependence of the critical crack velocity on the critical frequency, at which the IG-BTG transition occurs, undergoes an abrupt reversal as the critical frequency increases above about 0.1 Hz. Mechanisms potentially responsible for this change in frequency dependency are discussed in the context of the critical hydrogen model. The transition from low to intermediate frequency behavior is speculated to be due to a change in the critical distance from microstructural control, for frequencies at or below 0.1 Hz, to control by the critical hydrogen criterion at higher frequencies. The low frequency behavior is discussed relative to the transition from static load stress corrosion cracking to low frequency corrosion fatigue, which occurs as cyclic frequency increases above zero.

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James, L. A. « The Effect of Temperature and Cyclic Frequency Upon Fatigue Crack Growth Behavior of Several Steels in an Elevated Temperature Aqueous Environment ». Journal of Pressure Vessel Technology 116, n^o 2 (1 mai 1994) : 122–27. http://dx.doi.org/10.1115/1.2929565.

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The fatigue crack propagation (FCP) behavior of several ASTM A302-B and A508-2 steels was characterized in deaerated elevated temperature aqueous environment. FCP behavior was determined over the range 121°C to 343°C at a constant value of ΔK, stress ratio, and load rise time. A complex response of FCP rates as a function of temperature was observed, and this is discussed in the light of similar results developed by others within the nuclear industry. Corrosion potentials (referenced to the standard hydrogen electrode) were measured for each of the steels over the above temperature range and comparisons are made to the observed FCP behavior. Cyclic frequency effects were studied at two temperatures, 149°C and 243°C, and these are analyzed within the “time domain” format first suggested by Shoji et al. The results, when expressed in the time domain format, clearly show regions where environmentally assisted cracking (EAC) occurs, and regions where EAC does not occur. A “threshold” for EAC was noted at 149°C, and the possibility of an EAC threshold was observed at 243°C.

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de Castro, Jaime Tupiassú Pinho, Rodrigo Vieira Landim et Marco Antonio Meggiolaro. « Defect tolerance under environmentally assisted cracking conditions ». Corrosion Reviews 33, n^o 6 (1 novembre 2015) : 417–31. http://dx.doi.org/10.1515/corrrev-2015-0070.

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AbstractNotch sensitivity effects under environmentally assisted cracking (EAC) conditions have been recently quantified considering the tolerance to short cracks that may start at their tips and become nonpropagating after growing for a while, a behavior that depends on the stress gradients ahead of the notch tips and on the basic material resistances to crack initiation and propagation inside an aggressive medium. This model can provide a powerful alternative design tool for the pass/nonpass criterion traditionally used to deal with such mechanical-chemical problems, since it properly considers and quantifies the stress analysis issues that affect them. The model uses the analogy between the notch sensitivity behavior under fatigue and under EAC conditions, so it quantifies how the stress gradient around the notch tips affects the tolerance to mechanically short cracks that depart from there, considering the characteristics of the loading and of the notch geometry, as well as the basic material properties inside the given environment, expressed by its EAC resistances to crack initiation from a smooth surface SEAC and to crack propagation KIEAC, without the need for any data fitting parameter. Moreover, since this model has been validated by proper tests, it can be used to propose a defect-tolerant design criterion under EAC conditions that includes the unavoidable notch effects always present in actual structural components.

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James, L. A., H. B. Lee, G. L. Wire, S. R. Novak et W. H. Cullen. « Corrosion Fatigue Crack Growth in Clad Low-Alloy Steels—Part II : Water Flow Rate Effects in High-Sulfur Plate Steel ». Journal of Pressure Vessel Technology 119, n^o 3 (1 août 1997) : 255–63. http://dx.doi.org/10.1115/1.2842302.

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Corrosion fatigue crack propagation tests were conducted on a high-sulfur ASTM A302-B plate steel overlaid with weld-deposited Alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 22.8–27.3 mm, and depths of 10.5–14.1 mm. The experiments were initiated in a quasi-stagnant low-oxygen (O2 < 10 pph) aqueous environment at 243°C, under loading conditions (ΔK, R, cyclic frequency) conducive to environmentally assisted cracking (EAC) under quasi-stagnant conditions. Following fatigue testing under quasi-stagnant conditions where EAC was observed, the specimens were then fatigue tested under conditions where active water flow of either 1.7 m/s or 4.7 m/s was applied parallel to the crack. Earlier experiments on unclad surface-cracked specimens of the same steel exhibited EAC under quasi-stagnant conditions, but water flow rates at 1.7 m/s and 5.0 m/s parallel to the crack mitigated EAC. In the present experiments on clad specimens, water flow at approximately the same as the lower of these velocities did not mitigate EAC, and a free stream velocity approximately the same as the higher of these velocities resulted in sluggish mitigation of EAC. The lack of robust EAC mitigation was attributed to the greater crack surface roughness in the cladding interfering with flow induced within the crack cavity. An analysis employing the computational fluid dynamics code, FIDAP, confirmed that frictional forces associated with the cladding crack surface roughness reduced the interaction between the free stream and the crack cavity.

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Van Der Sluys, W. A., et R. H. Emanuelson. « Cyclic Crack Growth Behavior of Reactor Pressure Vessel Steels in Light Water Reactor Environments ». Journal of Engineering Materials and Technology 108, n^o 1 (1 janvier 1986) : 26–30. http://dx.doi.org/10.1115/1.3225836.

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During normal operation light water reactor (LWR) pressure vessels are subjected to a variety of transients resulting in time varying stresses. Consequently, fatigue and environmentally assisted fatigue are growth mechanisms relevant to flaws in these pressure vessels. In order to provide a better understanding of the resistance of nuclear pressure vessel steels to flaw growth process, a series of fracture mechanics experiments were conducted to generate data on the rate of cyclic crack growth in SA508-2 and SA533B-1 steels in simulated 550°F Boiling Water Reactor (BWR) and 550°F Pressurized Water Reactor (PWR) environments. Areas investigated over the course of the test program included the effects of loading frequency and R ratio (Kmin/Kmax) on crack growth rate as a function of the stress intensity factor (ΔK) range. In addition, the effect of sulfur content of the test material on the cyclic crack growth rate was studied. Cyclic crack growth rates were found to be controlled by ΔK, R ratio, and loading frequency. The sulfur impurity content of the reactor pressure vessel steels studied had a significant effect on the cyclic crack growth rates. The Higher growth rates were always associated with materials of higher sulfur content. For a given level of sulfur, growth rates were higher in a 550°F simulated BWR environment than in a 550°F simulated PWR environment. In both environments cyclic crack growth rates were a strong function of the loading frequency. Further, the loading frequency at which the highest cyclic crack growth rate was observed was found to be a function of the applied ΔK level. In most cases, all cyclic crack growth rates were on or under the ASME Section XI high R water reference flaw growth line and above the Section XI air reference flaw growth line, supporting the position of these lines on the growth rate–ΔK level graph.

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Arthyka Palifiana, Dheska, et Ratih Kumoro Jati. « HUBUNGAN ANTARA TINGKAT STRES DENGAN KUALITAS TIDUR PADA WARGA BINAAN DI LEMBAGA PEMASYARAKATAN KLAS IIA YOGYAKARTA ». MEDIA ILMU KESEHATAN 7, n^o 1 (16 novembre 2019) : 28–33. http://dx.doi.org/10.30989/mik.v7i1.220.

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Background: To have rest or to sleep is basic need that needed by everyone. To have enough rest or sleep will make body functioned optimally. By sleeping people can restore or to rest the physical after whole day activities, it can reduce stress and anxiety. It also improve concentration and improve ability when doing daily activities. Factors that affect quality and quantity of sleep include ill, fatigue, environment, lifestyle, emotional stress, diet, smoking, stimulant, alcohol, and motivation. The stress level on assisted citizen of woman’s prisoner will be more severe than who are not in prison so as stress can be overcome then the quality of sleep becomes better. Objective:To know the correlation between stress levels and sleep quality on assisted people in woman Penitentiary class II A Yogyakarta. Methods: The research was conducted at women's prison class II A Yogyakarta. Research population was 117 women prisoners. The sample was 50 women prisoners. Type of the research was descriptive analytic research with cross sectional design. Statistical analysis used chi square. The sampling technique used purposive sampling. Results: The stress level was mostly in high category as many as 17 respondents experienced stress (34%). Sleep quality of the respondents were mostly in bad category as many as 38 respondents (76%). There is a correlation between stress level and sleep quality on women prisoners in Penitentiary class II A Yogyakarta with p-value (0.033). Conclusion: There is a correlation between stress level and sleep quality on women prisoners in Penitentiary class II A Yogyakarta. Keywords: Stress level, sleep quality, assisted people, penitentiary

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Palifiana, Dheska Arthyka, et Ratih Kumorojati. « HUBUNGAN ANTARA TINGKAT STRES DENGAN KUALITAS TIDUR PADA WARGA BINAAN DI LEMBAGA PEMASYARAKATAN KLAS IIA YOGYAKARTA ». Media Ilmu Kesehatan 7, n^o 1 (30 avril 2018) : 28–33. http://dx.doi.org/10.30989/mik.v7i1.262.

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Background: To have rest or to sleep is basic need that needed by everyone. To have enough rest or sleep will make body functioned optimally. By sleeping people can restore or to rest the physical after whole day activities, it can reduce stress and anxiety. It also improve concentration and improve ability when doing daily activities. Factors that affect quality and quantity of sleep include ill, fatigue, environment, lifestyle, emotional stress, diet, smoking, stimulant, alcohol, and motivation. The stress level on assisted citizen of woman’s prisoner will be more severe than who are not in prison so as stress can be overcome then the quality of sleep becomes better. Objective:To know the correlation between stress levels and sleep quality on assisted people in woman Penitentiary class II A Yogyakarta. Methods: The research was conducted at women's prison class II A Yogyakarta. Research population was 117 women prisoners. The sample was 50 women prisoners. Type of the research was descriptive analytic research with cross sectional design. Statistical analysis used chi square. The sampling technique used purposive sampling. Results: The stress level was mostly in high category as many as 17 respondents experienced stress (34%). Sleep quality of the respondents were mostly in bad category as many as 38 respondents (76%). There is a correlation between stress level and sleep quality on women prisoners in Penitentiary class II A Yogyakarta with p-value (0.033). Conclusion: There is a correlation between stress level and sleep quality on women prisoners in Penitentiary class II A Yogyakarta. Keywords:Stress level, sleep quality, assisted people, penitentiary

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Kaiser, Trent M. V., Victor Y. B. Yung et Russ M. Bacon. « Cyclic Mechanical and Fatigue Properties for Oil-Country-Tubular-Goods Materials ». SPE Journal 13, n^o 04 (1 décembre 2008) : 480–86. http://dx.doi.org/10.2118/97775-pa.

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Summary This paper describes differences between actual material behavior and idealizations used for modeling purposes and discusses some of the implications for interpreting model predictions. Much of the design for well structures subjected to high-amplitude cyclic loading is based on material assumptions that extrapolate strength properties from uniaxial, tensile tests to conditions where multiaxial, cyclic stresses are imposed. This paper presents results from cyclic testing on a common oil-country-tubular-goods (OCTG) material and demonstrates differences between the physical behavior measured under cyclic loading conditions and theoretical behavior extrapolated by numerical modeling. Modeling theories for plastic deformation are discussed with their limitations and relevance in a cyclic-loading environment. The implications of these limitations for design choices in thermal wells also are discussed with example applications of cyclic material behavior and fatigue-life prediction. Material fatigue properties for the high-amplitude, low-cycle application of thermal operations have not been investigated in much depth previously, particularly for OCTG. Along with characterizing cyclic mechanical properties, the tests discussed here also assessed the low-cycle fatigue properties of the sample OCTG steel. The consistent fatigue measurements, combined with analysis results using representative cyclic mechanical properties, can provide a basis for estimating fatigue life. Depending on analysis-model assumptions, substantial variation in predicted fatigue life can occur; therefore, exact fatigue-life predictions are not anticipated. The primary value in such modeling is in evaluating the relative effectiveness of mitigation options for extending well life. Introduction Most thermal enhanced-oil-recovery (EOR) wells in western Canada operate using either the cyclic-steam-stimulation (CSS) or the steam-assisted-gravity-drainage (SAGD) method. In both methods, operational factors result in thermal cycles being imposed on the well structures, particularly in the intermediate casing (Placido et al. 1997). Thermal expansion is constrained by the formation and cement in CSS and SAGD wells, producing loads that exceed the yield strength of the tubulars when the well is heated. Localization mechanisms also might amplify the strain magnitude, imposing additional plastic fatigue load at discrete locations along the well structure. Thermal-well casing designs have evolved during more than 30 years of operating experience, and much of the computer modeling that describes casing performance is based on measured uniaxial tensile material properties that are extrapolated to multidimensional cyclic behavior through engineering models. Cyclic material-properties data are sparse, particularly in the temperature regime common in thermal-recovery wells. Furthermore, plastic fatigue-life information for materials commonly used in well construction is difficult to obtain. Such information, however, is required to make reliable predictions of certain deformation mechanisms and the associated fatigue life for wells exposed to cyclic, thermally imposed loading. A test program for characterizing cyclic material properties was implemented to evaluate both cyclic mechanical properties and low-cycle fatigue life. Test-result consistency indicates a reliable material characterization that can be applied in constitutive analysis models and component-life assessments. The observed cyclic-stress-strain material behavior also demonstrates different characteristics from those predicted through engineering models using uniaxial monotonic material properties for input. This has important implications for thermal-well design and operations.

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Chen, Ming Ya, Wei Wei Yu, Jin Hua Shi, Rong Shan Wang, Lv Feng, Fei Xue et Zhi Lin Chen. « Structural Integrity for the RPV of French NPP during the LRA ». Applied Mechanics and Materials 853 (septembre 2016) : 453–57. http://dx.doi.org/10.4028/www.scientific.net/amm.853.453.

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Most of the French Nuclear Power Plants (NPPs) are currently embarking upon efforts to renew their operating license, while the pressurized thermal shock (PTS) events and environmentally assisted fatigue (EAF) pose potentially significant challenges to the structural integrity of the reactor pressure vessel (RPV) which has the potential to be NPP life-limiting conditions. In the assessment of the PTS events, the deterministic fracture mechanics (DFM) is still used as the basic mechanics in most countries except for the USA. While the maximum nil-ductility-transition temperature (RTNDT) is about 80°C for 54 French RPVs after 40 years operation, the maximum allowable RTNDT is only about 70 oC and 80 oC for the typical PTS events in the IAEA and NEA reports, respectively. On the other hand, the effects of light water reactor (LWR) environmental (other than moderate environment in the code) were not considered in the original design, while the effects of LWR environmental are needed to be considered in the LRA according to the USA regulations. In this paper, the challenges of the PTS and EAF are discussed, and some suggestions are also given for the LRA

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Abbas, Muntazir, et Mahmood Shafiee. « Structural Health Monitoring (SHM) and Determination of Surface Defects in Large Metallic Structures using Ultrasonic Guided Waves ». Sensors 18, n^o 11 (15 novembre 2018) : 3958. http://dx.doi.org/10.3390/s18113958.

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Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws.

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Krausz, Alex S., Xijia Wu, Zhiwen Lian et Klara Krausz. « On the Constitutive Law of Environment Assisted Fatigue : The Physical Meaning of the Paris Iype Equations / Die konstitutive Gleichung für die umgebungsinduzierte Ermüdung : Die physikalische Bedeutung der Paris-Gleichungen. » International Journal of Materials Research 83, n^o 5 (1 mai 1992) : 356–63. http://dx.doi.org/10.1515/ijmr-1992-830513.

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MATHIS, Aude, Thierry MILLOT, Vincent BRANGER, Remy MULLER et Jean-Yves GUENEHEUX. « Tribological functionalization of titanium alloys by Micro-Arc Oxidation for marine applications ». MATEC Web of Conferences 321 (2020) : 09001. http://dx.doi.org/10.1051/matecconf/202032109001.

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Micro-arc Oxidation (MAO) process is a plasma assisted electrochemical process, which allows formation of ceramic-like dry oxides on top of light alloys surfaces. The good corrosion resistance as well as the low density of titanium alloys are recognized and so required for conception of structural parts in marine environment. However, their tribological behaviour reveals an important tendency to stick-slip phenomenon, which makes use of these alloys for dynamic contact mechanisms difficult. Through the MAO project from IRT M2P, formation of a MAO coating composed of aluminium titanate has been investigated to improve tribological behaviour of a commercially pure titanium (Grade 2) and an α+β alloy (TA6V, Grade 5). Pin-on-disc testing has been carried out to evaluate friction coefficient and the presence or not of stick-slip phenomenon in various contact configurations (involving non-treated titanium surfaces, MAO treated surfaces, with steel or titanium balls …) in dry or artificial seawater media. Those test campaigns are completed by evaluation of fatigue behaviour, and tribological testing on a demonstrator. Finally, this study highlights influence of MAO coating on diminishing (to removed) stick-slip phenomenon, accompanied by a reduction of friction coefficient, whatever the kind of contact (single treated surface or both ones) and the medium.

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Kujawski, Daniel, et Phani C. R. Sree. « Modeling of environmentally assisted fatigue crack growth behavior ». Corrosion Reviews 33, n^o 6 (1 novembre 2015) : 351–59. http://dx.doi.org/10.1515/corrrev-2015-0064.

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AbstractIt is well recognized that environment has a significant role on the failure of mechanically loaded structures. In most cases of cyclic loading, fatigue crack growth (FCG) behavior exhibits lower threshold and faster growth rate in air than in vacuum. It is well documented that the effect of loading frequency on FCG behavior can be more pronounced in aggressive environment/material systems. This is seen in the Kmax term of the FCG. On the other hand, a weak dependence of FCG behavior with R ratio in inert environment indicates that a crack extension is governed mainly by ΔK. Existing experimental data indicate that the actual crack extension per cycle is associated with the rising part of the load cycle than the unloading part. In this paper, the synergetic role of environment and mechanical loading on crack growth behavior is considered to see their roles on FCG. In this article, we attempt to model how crack extension interplays between a crack-tip opening and crack-tip blunting angle associated with the applied load and environment, respectively. To support such a model for discussion, we have selected limited FCG data taken from literature corresponding to different environments ranging from vacuum to air and NaCl solution for a number of alloys and with different specimens geometries. We are also not discussing innate mechanisms for each alloy, due to space concerns.

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Phadte, Saloni, Sharvi Shenvi, Siddhant Prabhudesai et Jai Sawant. « Electrically Assisted Bicycle Adapted to Urban Mobility ». International Journal for Research in Applied Science and Engineering Technology 10, n^o 8 (31 août 2022) : 423–26. http://dx.doi.org/10.22214/ijraset.2022.46205.

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Abstract: Traffic congestion, energy conservation and environmental issues are fuelling the interest in light electric vehicles. In particular, electric vehicles are compelling because of their low cost, ease of use, lightweight, and extremely small footprint. This project deals with design and fabrication of a low-cost portable electric bicycle kit which makes use of electric energy as the primary source and can be mounted on any non-geared bicycle. It has two modes of drive; one is manual i.e. by pedalling and the other one is electric by using electric power from a DC battery. The kit consists of 250W PMDC motor which is powered by a 24V Li-ion battery. One of the major disadvantages of traditional bicycle is that it increases rider’s fatigue during long distance travel. The electric bicycle provides a better riding experience as it runs on electric power thereby reducing the rider’s fatigue. This helps in travelling longer distances comfortably. The electric bicycle is also faster compared to a traditional bicycle. It is also an environment friendly means of transportation as it does not depend on fossil-fuels for energy. The expected range of the bicycle is around 30-35 km on a single charge and expected speed is 20 kmph.

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Petit, Jean, Christine Sarrazin-Baudoux et Michel Gerland. « Influence of Microstructure, Environment and Temperature on Fatigue Crack Propagation in 2XXX Aluminium Alloys ». Key Engineering Materials 592-593 (novembre 2013) : 22–29. http://dx.doi.org/10.4028/www.scientific.net/kem.592-593.22.

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Aluminum alloys, widely used for constitutive parts of aircrafts are confronted to a wide range of temperature depending on altitude and climate, from room temperature on the ground down to some 223K at high altitude. The fatigue crack growth behavior of two new generation aluminum alloys, 2024A in T351 temper and 2022 in T351 and T851 tempers, have been investigated at both temperatures. It is shown that temperature and air humidity do not affect the crack growth resistance of the peak aged 2022 while these two parameters widely influence the crack growth in the under-aged alloys which exhibit in cold air a crystallographic retarded propagation similar to that in vacuum. The respective role of microstructure, temperature, atmosphere residual humidity and crack closure is discussed on the basis of a preexisting modeling framework for environmentally assisted fatigue.

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Loew, Stefan, et Carlo L. Bottasso. « Lidar-assisted model predictive control of wind turbine fatigue via online rainflow counting considering stress history ». Wind Energy Science 7, n^o 4 (3 août 2022) : 1605–25. http://dx.doi.org/10.5194/wes-7-1605-2022.

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Abstract. The formulation of parametric online rainflow counting implements the standard fatigue estimation process and a stress history in the cost function of a model predictive controller. The formulation is tested in realistic simulation scenarios in which the states are estimated by a moving horizon estimator and the wind is predicted by a lidar simulator. The tuning procedure for the controller toolchain is carefully explained. In comparison to a conventional model predictive controller (MPC) in a turbulent wind setting, the novel formulation is especially superior with low lidar quality, benefits more from the availability of wind prediction, and exhibits a more robust performance with shorter prediction horizons. A simulation excerpt with the novel formulation provides deeper insight into the update of the stress history and the fatigue cost parameters. Finally, in a deterministic gust setting, both the conventional and the novel MPC – despite their completely different fatigue costs – exhibit similar pitch behavior and tower oscillations.

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Arrieta, Sergio, Francisco Javier Perosanz, Jose Miguel Barcala, Maria Luisa Ruiz et Sergio Cicero. « Using Direct Current Potential Drop Technique to Estimate Fatigue Crack Growth Rates in Solid Bar Specimens under Environmental Assisted Fatigue in Simulated Pressurized Water Reactor Conditions ». Metals 12, n^o 12 (6 décembre 2022) : 2091. http://dx.doi.org/10.3390/met12122091.

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The direct current potential drop (DCPD) technique may be used in crack propagation tests to measure the crack growth rate (CGR). Potential probes attached to the specimen allow the variation of the crack length to be estimated. In this research, the DCPD technique using one single potential probe was applied to solid bar specimens (i.e., without any initial notch or crack) subjected to low-cycle fatigue testing in a simulated pressurized water reactor (PWR) environment. This particular analysis had two associated difficulties, the first one being the fact that crack initiation sites are not known beforehand, and the second one consisting in the experimental difficulties and conditioning factors associated with the simulation of the PWR environment. Nine solid bar specimens were tested to fatigue failure under different strain amplitudes and frequencies, while also measuring the corresponding DCPD signal during the fatigue process. It was observed that the initiation of multiple cracks was detected by the DCPD measurements. Moreover, as fatigue continued, one of the cracks became dominant and progressed to cause the specimen failure. The DCPD technique allowed the average CGR of the dominant crack to be estimated. Finally, the obtained average CGRs were validated by comparing them with average CGRs derived from striation spacing measurements, obtained from scanning electron microscopy (SEM) and from literature values gathered in the NUREG/CR-6909 document.

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Ma, Kai, Jinyang Zheng, Zhengli Hua, Chaohua Gu, Ruiming Zhang et Yayu Liu. « Hydrogen assisted fatigue life of Cr–Mo steel pressure vessel with coplanar cracks based on fatigue crack growth analysis ». International Journal of Hydrogen Energy 45, n^o 38 (juillet 2020) : 20132–41. http://dx.doi.org/10.1016/j.ijhydene.2020.05.034.

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Takakuwa, O., et H. Soyama. « Suppression of hydrogen-assisted fatigue crack growth in austenitic stainless steel by cavitation peening ». International Journal of Hydrogen Energy 37, n^o 6 (mars 2012) : 5268–76. http://dx.doi.org/10.1016/j.ijhydene.2011.12.035.

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