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1
Neuberg, Or, and Nitai Drimer. "Fatigue limit state design of fast boats." Marine Structures 55 (September 2017): 17–36. http://dx.doi.org/10.1016/j.marstruc.2017.05.002.
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Lotsberg, I. "Recent advances on fatigue limit state design for FPSOs." Ships and Offshore Structures 2, no. 1 (January 2007): 49–68. http://dx.doi.org/10.1533/saos.2006.0145.
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Zhang, Zhongke, Yang Yu, Huaxia Zhao, and Hui Tong. "Effect of Loading Methods on the Fatigue Properties of Dissimilar Al/Steel Keyhole-Free FSSW Joints." Materials 13, no. 19 (September 23, 2020): 4247. http://dx.doi.org/10.3390/ma13194247.
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The energy evolution, fatigue life and failure behaviour of dissimilar Al/steel keyhole-free Friction stir spot welding (FSSW) joints were studied under different fatigue loads. The absorption energy of fatigue fracture, the fracture mechanism and the sensitivity of the fatigue limits to the fatigue load parameters were analysed. It was found that the stress ratio R determines the fatigue limit Ff, while the fatigue limit Ff is not sensitive to the loading frequency. The high-frequency fatigue load will increase the displacement deformation μ and fatigue fracture absorption energy Ea of the spot-welded joint, which are larger under asymmetric fatigue loading than those under symmetrical fatigue loading. At the same time, the symmetrical fatigue load can form the steady-state hysteresis loop, while asymmetric fatigue loading cannot, but asymmetric fatigue loading exhibits the displacement increment of fatigue softening. The fracture failure of spot-welded joints is a multiple crack source and the mixed-mode of ductile and brittle fracture mechanism, which exhibits typical fatigue striations in the fatigue fractures.
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Тотай, Анатолий, and Anatoliy Totay. "ANALYTICAL APPROACH TO TECHNOLOGICAL SUPPORT OF FATIGUE LIMIT." Bulletin of Bryansk state technical university 2019, no. 3 (March 27, 2019): 13–20. http://dx.doi.org/10.30987/article_5c8b5cea063335.55319966.
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In the paper on the basis of the theory of metal plastic deformation there are obtained analytical de-pendences of dislocations critical density and cycle number up to destruction caused by factors technological impact upon the surface under working.
For the first time in complex there are taken into account such physical characteristics as an effort, temperature and speed of deformation in the area of cutting and strengthening.
A tie between such parameters of surface layer state as a steel grain size and dislocations density is defined.
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Szerszen, Maria M., and Andrzej S. Nowak. "Fatigue Evaluation of Steel and Concrete Bridges." Transportation Research Record: Journal of the Transportation Research Board 1696, no. 1 (January 2000): 73–80. http://dx.doi.org/10.3141/1696-10.
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The fatigue limit state is one of the important considerations in the design of bridges. Accumulated load cycles can cause cracking or even failure. An approach to evaluation of steel and concrete bridges with regard to fatigue is presented. The method for prediction of the remaining life of a bridge superstructure is based on the load model and the procedure to estimate fatigue degradation of materials. In the case of steel girders, degradation of material is considered using S-N curves. For reinforced concrete beams, degradation of concrete in the compressive zone is described by the rheological fatigue model. Reliability analysis is performed for the fatigue limit state function of flexure. Prediction of the remaining fatigue life for steel and concrete beams is illustrated on examples of existing bridge girders.
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Moran, B., Y. Xu, and J. D. Achenbach. "Limit-State Surface Element Method: Application to Fatigue Reliability with NDE Inspections." Journal of Engineering Mechanics 126, no. 7 (July 2000): 684–92. http://dx.doi.org/10.1061/(asce)0733-9399(2000)126:7(684).
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Hou, Shanqin, and Jinquan Xu. "A phenomenological life evaluation method for corrosion fatigue." Corrosion Reviews 35, no. 2 (July 26, 2017): 75–83. http://dx.doi.org/10.1515/corrrev-2016-0063.
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AbstractConsidering interacted damage accumulations induced by corrosion, cyclic fatigue, and stress corrosion cracking, a phenomenological corrosion fatigue (CF) life evaluation formula has been proposed. A concept of nominal CF limit has been introduced, which indicates whether cyclic damage accumulation is active or not. It is found that cyclic fatigue damage accumulation enhanced by corrosion is the dominative damage under relatively high stress amplitudes (compared to the nominal limit), whereas, under low stress amplitudes, corrosion damage accumulation would become the dominative one. Stress amplitudes below the nominal fatigue limit would lead to CF too due to corrosion damage accumulation, which can finally make the effective amplitude larger than nominal limit. Once the parameters included in formula have been determined by uniaxial tests, CF life under any complicated stress state could be estimated in a unified way.
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Zhong, Liqiong, Hao Hu, Yilong Liang, and Chaowen Huang. "High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature." Metals 9, no. 1 (December 21, 2018): 13. http://dx.doi.org/10.3390/met9010013.
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In this paper, the high cycle fatigue performance of solid solution state and aged Inconel 718 superalloys was studied at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the original structural features and fatigue deformation features of two kinds of alloys. SEM, laser scanning confocal microscopy, and electron backscatter diffraction (EBSD) were used to analyze the secondary fracture features of the fatigue fracture morphology and fatigue fracture profile. The results showed that the aging treatment significantly affected the strength and plasticity of the alloy, which in turn affected the fatigue performance of the alloy. After the aging treatment, the yield strength σs and the tensile strength σb of the Inconel 718 alloy increased by 152% and 65.9%, respectively, compared with those of the solid solution state, but the rate of elongation δ and rate of contraction in the cross-section area φ decreased by 63.7% and 52.3%, respectively. The fatigue limit of the aged state was lower than that of the solid solution state by 6.3%. The quadratic function relationship between the high cycle fatigue limit σ−1 and the tensile strength σb of the Inconel 718 superalloy at room temperature was σ−1 = σb · (0.869−3.67 × 10−4 · σb). An analysis of the fatigue fracture mechanism showed that the fatigue fractures before and after aging were all initiated in the grains oriented relatively unfavorably on the surface of the sample, with a mixture of intergranular and transgranular propagation after the transgranular propagation of several grains. The higher plasticity of the solid solution state Inconel 718 alloy resulted in a large number of slip deformation zones under high cycle fatigue loads, and the plastic deformation was relatively uniform. The lengths of the secondary fractures were as high as 120 μm, which formed the single-source plastic fatigue fracture that promoted an increase in the fatigue limit. After aging treatment, the higher strength of the Inconel 718 alloy made dislocation slip difficult under high cycle fatigue loads, and the plasticity compatible deformation capability was poor. When local dislocations slipped to the intragranular γ” phase, γ’ phase, or interfaces with nonmetallic compounds (NMCs), plugging occurred. The degree of stress concentration increased, causing the initiation of fatigue fracture; the secondary fracture was approximately 20 μm. Brittle cleavage due to multiple sources significantly reduced the fatigue limit.
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Collette, Matthew, and Atilla Incecik. "An Approach for Reliability-Based Fatigue Design of Welded Joints on Aluminum High-Speed Vessels." Journal of Ship Research 50, no. 01 (March 1, 2006): 85–98. http://dx.doi.org/10.5957/jsr.2006.50.1.85.
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Fatigue cracks are an ongoing problem for aluminum high-speed vessels, and preventing fatigue cracks caused by wave loading is expected to be a significant challenge for future aluminum high-speed ferries and military vessels. To aid in this effort, a hot-spot fatigue design approach using first-order reliability methods (FORM) is constructed. Two different limit state functions are investigated, and the accuracy and consistency of the FORM method for the highly nonlinear fatigue limit state equations are evaluated through a comparison with Monte Carlo simulation results. The sensitivity of the resulting safety index to changes in the input variables, and their uncertainties, are presented graphically. The method is compared to existing design standards for four simple structural details.
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Scott-Emuakpor, Onome, M. H. Herman Shen, Tommy George, Charles J. Cross, and Jeffrey Calcaterra. "Development of an Improved High Cycle Fatigue Criterion." Journal of Engineering for Gas Turbines and Power 129, no. 1 (March 1, 2004): 162–69. http://dx.doi.org/10.1115/1.2360599.
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An integrated computational-experimental approach for prediction of total fatigue life applied to a uniaxial stress state is developed. The approach consists of the following elements: (1) development of a vibration based fatigue testing procedure to achieve low cost bending fatigue experiments and (2) development of a life prediction and estimation implementation scheme for calculating effective fatigue cycles. A series of fully reversed bending fatigue tests were carried out using a vibration-based testing procedure to investigate the effects of bending stress on fatigue limit. The results indicate that the fatigue limit for 6061-T6 aluminum is approximately 20% higher than the respective limit in fully reversed tension-compression (axial). To validate the experimental observations and further evaluate the possibility of prediction of fatigue life, an improved high cycle fatigue criterion has been developed, which allows one to systematically determine the fatigue life based on the amount of energy loss per fatigue cycle. A comparison between the prediction and the experimental results was conducted and shows that the criterion is capable of providing accurate fatigue life prediction.
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Sous, Christopher, Henrik Wünsch, Georg Jacobs, and Christoph Broeckmann. "Prediction of fatigue limit of journal bearings considering a multi-axial stress state." Industrial Lubrication and Tribology 68, no. 3 (April 11, 2016): 430–38. http://dx.doi.org/10.1108/ilt-08-2015-0119.
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Purpose The purpose of this paper is to investigate the applicability of the quadratic failure hypothesis (QFH) on journal bearings coated with a white metal sliding layer on the prediction of safe and unsafe operating conditions. The hypothesis covers operation conditions under static and dynamical loading. Design/methodology/approach Material tests and elastohydrodynamic, as well as structural, simulations were conducted to provide the required input data for the failure hypothesis. Component samples were tested to verify the results of the QFH. Findings The load bearing capacity of journal bearings was analysed for different operating conditions by the use of the QFH. Results allow for the identification of critical and non-critical loading conditions and are in accordance with component test results. Originality/value Today’s design guidelines for journal bearings do not consider a multi-axial stress state and actual stress distribution. The applied hypothesis enables consideration of multiaxiality inside the sliding surface layer, as well as determining the location of bearing fatigue due to material overload.
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Saito, Ryoichi, Nao-Aki Noda, Yoshikazu Sano, Jian Song, Takeru Minami, Yuuka Birou, Arata Miyagi, and Yinsa Huang. "Fatigue Strength Analysis and Fatigue Damage Evaluation of Roller Chain." Metals 8, no. 10 (October 18, 2018): 847. http://dx.doi.org/10.3390/met8100847.
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This paper deals with the roller chain commonly used for transmission of mechanical power on many kinds of industrial machinery, including conveyors, cars, motorcycles, bicycles, and so forth. It consists of a series of four components called a pin, a bush, a plate, and a roller, which are driven by a sprocket. To clarify the fatigue damage, in this paper, the finite element method (FEM) is applied to those components under three different types of states, that is, the press-fitting state, the static tensile state, and the sprocket-engaging state. By comparing those states, the stress amplitude and the average stress of each component are calculated and plotted on the fatigue limit diagram. The effect of the plastic zone on the fatigue strength is also discussed. The results show that the fatigue crack initiation may start around the middle inner surface of the bush. As am example, the FEM results show that the fatigue crack of the inner plate may start from a certain point at the hole edge. The results agree with the actual fractured position in roller chains used in industry.
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Škaloud, Miroslav, and Marie Zörnerová. "THE FATIGUE BEHAVIOUR OF THE BREATHING WEBS OF STEEL BRIDGE GIRDERS." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 11, no. 4 (December 31, 2005): 323–36. http://dx.doi.org/10.3846/13923730.2005.9636363.
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The limit state of thin‐walled steel girders subjected to many times repeated loading is to a great extent affected by the cumulative damage process occurring in the girder webs “breathing” under the repeated loads. Based on experimental results obtained by the authors at the Institute of Theoretical and Applied Mechanics in Prague, (i) various approaches to the definition of the fatigue limit state of the above girders are discussed, (ii) a number of potential design procedures suggested by other researchers validated and (iii) a set of S‐N curves, established by the writers so as to serve as a reliable tool for the fatigue analysis of thin‐walled girders with “breathing” webs, presented.
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Sharipov, Ravil, Sergey Zenin, Sergey Krylov, and Yuri Volkov. "Evaluation of methods for calculating reinforced concrete structural members for the fatigue limit state." Bulletin of Science and Research Center “Stroitelstvo”, no. 4(27)2020 (2020): 148–59. http://dx.doi.org/10.37538/2224-9494-2020-4(27)-148-159.
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В нормах по проектированию железобетонных конструкций зданий и сооружений (начиная с 1962 г. и по настоящее время) содержится методика расчета на выносливость, которая была составлена с учетом обобщения и анализа данных многочисленных экспериментально-теоретических исследований. Последующее использование данной методики в практике проектирования железобетонных конструкций показало, что при эксплуатации конструкций, рассчитанных с учетом требований по выносливости, разрушений не происходило. Вместе с тем, анализ показал отличие отечественной методики от подходов иностранных норм в части расчета по растянутой арматуре. Дальнейшие исследования показали некоторые неcовершенства нормативной методики расчета по растянутой арматуре (как ненапрягаемой, так и предварительно напряженной). С учетом данных проведенных расчет-но-теоретических исследований, а также в целях гармонизации с основными положениями расчета на усталость, принятого в нормах проектирования ряда ведущих стран, представляется полезным в расчете на усталость по растянутой арматуре наряду с максимальным напряжением в пределах цикла нагрузки учитывать и предельную амплитуду напряжений. В этой связи предполагается проведение актуализации существующей методики расчета на выносливость, которая будет дополнена новыми положениями расчета по растянутой арматуре. При актуализации методики наиболее правильным будет максимально учесть другие положения существующей методики. В частности, будет сохранен прежний подход к определению действующих напряжений в бетоне и арматуре, а также расчет на усталость по сжатому бетону.
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Gopkalo, A. P. "Evaluation of the limit state and cyclic life of structural materials under thermal fatigue." Strength of Materials 41, no. 1 (January 2009): 74–80. http://dx.doi.org/10.1007/s11223-009-9101-z.
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Cincotta, Molly C., Matthew M. Engelhard, Makela Stankey, and Myla D. Goldman. "Fatigue and fluid hydration status in multiple sclerosis: A hypothesis." Multiple Sclerosis Journal 22, no. 11 (August 20, 2016): 1438–43. http://dx.doi.org/10.1177/1352458516663854.
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Background: Fatigue is a prevalent and functionally disabling symptom for individuals living with multiple sclerosis (MS) which is poorly understood and multifactorial in etiology. Bladder dysfunction is another common MS symptom which limits social engagement and quality of life. To manage bladder issues, individuals with MS tend to limit their fluid intake, which may contribute to a low-hydration (LoH) state and fatigue. Objective: To evaluate the relationship between patient-reported MS fatigue, bladder dysfunction, and hydration status. Methods: We performed a prospective cross-sectional study in 50 women with MS. Participants submitted a random urine sample and completed several fatigue-related surveys. Using a urine specific gravity (USG) threshold of 1.015, we classified MS subjects into two groups: high-hydration (HiH) and LoH states. Results: LoH status was more common in MS subjects with bladder dysfunction. Statistically significant differences in self-reported Fatigue Performance Scale were observed between HiH and LoH subjects ( p = 0.022). USG was significantly correlated with fatigue as measured by the MS Fatigue Severity Scale (FSS) score ( r = 0.328, p = 0.020). Conclusion: Hydration status correlates with self-reported fatigue, with lower fatigue scores found in those with HiH status (USG < 1.015).
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Cheng, Jian Hua, Jian Min Xiong, and Jin Zhi Zhou. "Reliability Calculation of Design Point Method for Orthotropic Plate." Advanced Materials Research 639-640 (January 2013): 1029–32. http://dx.doi.org/10.4028/www.scientific.net/amr.639-640.1029.
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The design point method is a commonly-used method on fatigue reliability analysis. It is put forward, based on Palmgren-Miner linear fatigue damage accumulation rule, that the evaluation method of fatigue reliability for orthotropic plate in this article. It is analyzed the random variables of limit state equation of single component, established the three parameters of stress amplitude , fatigue life and constant , and derived the calculation method on reliability index of design point method, which would provide evidence for consequent design of Orthotropic Plate.
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Kim, Hyo Jin, Dong Jo Kim, Hyeong Cheol Lee, and Sang Ho Lee. "Damage Assessment of Steel Bridge Members by Fatigue Vulnerability Considering Corrosion and Traffic Variation with Time." Key Engineering Materials 348-349 (September 2007): 125–28. http://dx.doi.org/10.4028/www.scientific.net/kem.348-349.125.
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The fatigue vulnerability estimation method including the effects induced by the corrosion rate and the traffic variation with time has been proposed to evaluate the reduction of fatigue strength in steel bridge members. A fatigue limit state function considering corrosion and traffic variation is established to determine whether the steel bridge members have been damaged by both corrosion and fatigue or not. Monte-Carlo simulation is used for reliability analysis which provides the data used to obtain fatigue vulnerability curves. The results show that the damage accumulation induced by fatigue in steel bridges could be assessed by fatigue vulnerability curve considering influences of corrosion and traffic variation.
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Teng, Yuan Yuan, Da Shan Dong, and Hui Qing Qiu. "Comparative Analysis on the Allowable Stress and Limit State Methods of Crane Structure Design Standards at Home and Abroad." Advanced Materials Research 468-471 (February 2012): 559–64. http://dx.doi.org/10.4028/www.scientific.net/amr.468-471.559.
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This paper adopts the allowable stress and limit state methods of Chinese and European crane structure design standards(GB3811-2008 and FEM-1998 ), and illustrates correspondingly in detail the computing means on the overall checking of strength, static and dynamics stiffness, buckling of bar and plate, and fatigue. Taking a real crane as an example, according to the above three specifications, it designs the crane’s metal structure again, checks all aspects and guarantees the strength, buckling and fatigue indexes all reach 90 percent of the permissions, then comparative analyzes the new design parameters and checking indicators, combining failure probability obtained by PDS. It provides helpful and reference value for understanding the transition from the allowable stress to limit state method in design standards and the differences of theirs’ at home and abroad.
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Zou, Guang Ping, Qi Chao Xue, and Zhong Liang Chang. "The Fatigue Reliability Analysis of Stress Criterion in Multiaxial High Cycle Fatigue." Key Engineering Materials 417-418 (October 2009): 389–92. http://dx.doi.org/10.4028/www.scientific.net/kem.417-418.389.
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The stress criterion of multiaxial high cycle fatigue is a type of non-linear equation of high-order. It is used to predict the failure of fatigue in proportional torsion and bending loads. Soon-Bok Lee presented a new design criterion for fully reversed out-of phase torsion and bending. The values are randomized in different random distributions in Lee’s criterion formula. The correlations among random variables are considered and limit state equation is also established. This paper attempts to use First Order Reliability Method (FORM) and Second Order Reliability Method (SORM) to calculate the reliability of material fatigue in torsion and bending loads. The example is calculated and it is found that the failure probability estimated by using the SORM is more reliable than those of the FORM in multiaxial high cycle fatigue.
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Molokov, K. A., V. V. Novikov, and A. P. German. "Analytical model for assessing fatigue limit of welded joints of ferritic-pearlitic steels." Advanced Engineering Research 20, no. 3 (October 5, 2020): 225–34. http://dx.doi.org/10.23947/2687-1653-2020-20-3-225-234.
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Introduction. Microdefects and zones with stress concentration in welded joints cause fatigue macrocracks. Such damage is potentially dangerous, especially if the fatigue life of the structure is almost exhausted. In this case, the crack size is close to the critical value, and it is crucial to determine its length. The paper considers the development of an engineering analytical model for assessing the critical crack length and endurance limit of welded joints with the formed grain in the structure of ferrite-pearlitic steels after welding. Materials and Methods. The theory and methods of fracture mechanics at the mesoscale are used. A simple analytical dependence is obtained, which provides determining the critical dimensions of a macrocrack for ferrite-pearlite steels without using the Griffiths formula. . The calculation results of the critical crack lengths of various steels depending on their yield strength are presented. An analytical dependence of the endurance limit calculation for the most dangerous symmetric loading cycle, according to the standard set of mechanical characteristics and the average grain diameter of ferrite-pearlite steel, is presented. Results. Structural deformation analysis of the crack propagation process has been performed. On its basis, an engineering technique for assessing the endurance limit is developed. A mathematical model that enables to calculate the endurance limit and the critical crack length in the components of welded assemblies of large-sized facilities, considering periodic loads of a symmetrical cycle, is developed. Using this model, it is possible to estimate the degree of metal sensitivity to the original characteristics (yield stress, Poisson's ratio, grain diameter, relative constriction, Young's modulus, power-law hardening coefficient, etc.).Discussion and Conclusion. Under stresses corresponding to the steel endurance limit, the critical crack opening rates of the tip and edges approach each other. Energetically, this moment approximately corresponds to the transition of the crack to an unstable state. The accumulation of one-sided plastic deformations causes the limiting state of plasticity of the region adjacent to the crack tip and its avalanche-like or sharply accelerated motion. This critical area is interrelated with the grain diameter of the material, the characteristic of critical plasticity and the critical opening at the crack tip at the fatigue limit. The proposed analytical dependences can be used to assess the residual life and the fatigue limit of welded structures, the influence of various factors on the fatigue limit of welded joints of ferrite-pearlitic steels used in mechanical engineering, shipbuilding, pipeline transport, etc
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Fu, Hai, and Yilong Liang. "Study of the Surface Integrity and High Cycle Fatigue Performance of AISI 4340 Steel after Composite Surface Modification." Metals 9, no. 8 (August 6, 2019): 856. http://dx.doi.org/10.3390/met9080856.
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In the field of materials science, the fabrication of a material with severe surface plastic deformation and a good surface state is an issue encountered in the development of counterbalanced gradient materials. For this paper, AISI 4340 steel was first processed with abrasive water jet peening (AWJP) and then with ultrasonic surface rolling (USRE) to obtain a good surface state while maintaining large plastic deformation. The AISI 4340 steel composite surface was therefore modified, and the surface integrity and cycle fatigue performance were analyzed. The results show that the plastic deformation layer of the modified composite surface of the 4340 steel was 310 µm from the surface of the sample, the grain size 40 µm from the surface layer was refined to 70 nm, and the maximum surface roughness Ra is 0.06. The fatigue limit of the modified composite surfaces obtained by the tensile fatigue test was 595.7 MPa, which was 85.7 MPa higher than the 510 MPa fatigue limit of the unmodified matrix, indicating that the method of composite surface modification can produce a deep deformation layer while maintaining good surface conditions. The results show that work hardening caused by a composite surface treatment is the most important factor for improving the fatigue performance of materials.
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Kuzichkin, O. R., N. V. Dorofeev, A. V. Grecheneva, R. V. Romanov, and D. I. Surzhik. "Estimation of the probability of karst cavities collapse under technogenic cyclic loads below the fatigue limit." MATEC Web of Conferences 272 (2019): 01007. http://dx.doi.org/10.1051/matecconf/201927201007.
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The paper deals with the phenomenon of fatigue formation in soils over karst cavities under cyclic loading near the fatigue limit. A method is proposed for determining the stress state of the integumentary earth arising during the considered technogenic cyclic loads. Currently, the assessment of the possibility of karst cavities collapse is performed on the basis of static models, without taking into account the dynamic technogenic load. Especially in the case of slow cyclic loads of low intensity, which do not directly lead to collapse of the soil above the karst cavities. However, these actions change the bearing capacity of soils that are not taken into account at the exploration stage and are not laid in the project documentation for the construction of facilities in karst-dangerous areas. A technique for estimating pre-crisis states based on joint processing of active geoelectric and seismoacoustic geodynamic control signals is proposed.
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Bagmutov, V. P., N. G. Dudkina, I. N. Zakharov, M. D. Romanenk, and V. V. Chekunov. "Influence of structure and properties of surface layer on fatigue durability of hardened steels strengthened by combined electromechanical treatment." Izvestiya. Ferrous Metallurgy 62, no. 6 (June 28, 2019): 438–50. http://dx.doi.org/10.17073/0368-0797-2019-6-438-450.
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Using the example of hardened carbon steels (steel 45, U8), the effect of combination of various surface hardening technologies is considered (using electromechanical processing, surface plastic deformation, non-abrasive ultrasonic finishing and their combination) on changes in structural state and surface microhardness, cyclic durability of hardened specimens and fatigue failure mechanisms. The studies were carried out by the methods of optical and scanning electron microscopy and by microhardness and fatigue tests. It is shown that for the investigated steels in quenched state, a high-speed pulsed thermo-deformation effect during electromechanical processing is accompanied by an increase in the surface microhardness (by more than 50 %) and decrease in the fatigue limit (by 20 – 30 %). Such a change in properties is associated with formation in the surface layer of substantially non-equilibrium, inhomogeneous in chemical composition, ultradispersed phases with increased hardness. At the same time, in the near-surface metal volumes tempering processes of the hardened structure proceed with the formation of softening zones and tensile residual stresses, accompanied by a decrease in the microhardness in these zones and the fatigue limit of the specimens. Such effects reduce some of the materials performance characteristics during surface hardening. The ways to improve the properties of such products due to additional technological operations require further studies. Combined surface hardening (based on electromechanical processing, surface plastic deformation and non-abrasive ultrasonic finishing) of carbon steels allows, due to variations in the intensity of temperature and deformation effects, to purposefully change the structural-phase composition and stress-strain state of the surface and near-surface metal layers. As a result, it becomes possible to form a balanced complex of strength and fatigue characteristics of the samples, depending on the preliminary heat treatment of steel. The operations of surface plastic deformation and non-abrasive ultrasonic finishing after electromechanical hardening, due to intensive plastic deformation provide smoothing of the surface and healing of near-surface defects and allow correction of stress-strain state of the processed metal. It provides an increase in microhardness in the tempering zone by 20 – 25 % and the fatigue limit of the samples by 25 – 30 %.
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Zhang, Rong Ling, Qi Cai Wang, Li Na Ma, Jian Guo, and Shu Hong Liu. "Experimental Study and Evaluation on Bearing Capacity of Slab Culverts in Da-Qin Railway." Applied Mechanics and Materials 90-93 (September 2011): 1190–94. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.1190.
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Abstract. The experimental research on heavy haul railway existent diseases under double disadvantage fatigue load of special high stress level and multiple cycle index in da-qin railway, the bearing capacity of existing slab culverts are calculated and analyzed on ultimate limit state and serviceability limit state. According to 1:1 scale,laboratory test study on cover plate’s deflection, crack, strain of tensile steel about one piece of slab culvert in different static load and assess the cover plate’s initial state maximum carrying capacity;and for the other two pieces of cover plates, static load below 30t compression was applied until concrete cracking in order to carry on fatigue test for simulating axle load in heavy haul railway, to detect the bearing capacity of the plate and assess the service life of slab culvert. It puts forward some suggestions for the further research field in slab culvert and provides a theoretical support and practical experience for present situation and service life on existing heavy haul railway.
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Zou, Xiao Li. "Reliability Analysis of Fatigue Crack Growth with JC Method Based on Scientific Materials." Applied Mechanics and Materials 63-64 (June 2011): 882–85. http://dx.doi.org/10.4028/www.scientific.net/amm.63-64.882.
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Since the fatigue crack propagation process from initial size till final fracture is affected by lots of random factors, it is difficult to evaluate the fatigue reliability. Based on reliability theory, the first order second moment method ( JC method) is adopted to analyze and compute the fatigue reliability. To account for the uncertainties of material resistance, the parameters in the deterministic fatigue crack growth rate equation and material fracture toughness are taken as random variables with Normal distribution or Log-Normal distribution. Consequently, the limit state equation of fatigue crack growth is derived. The fatigue reliability index at any moment is calculated iteratively through JC method. As a computation example, the curve of fatigue crack growth reliability index with time is presented.
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Dureau, Clément, Marc Novelli, Mandana Arzaghi, Roxane Massion, Philippe Bocher, Yves Nadot, and Thierry Grosdidier. "On the Influence of Ultrasonic Surface Mechanical Attrition Treatment (SMAT) on the Fatigue Behavior of the 304L Austenitic Stainless Steel." Metals 10, no. 1 (January 8, 2020): 100. http://dx.doi.org/10.3390/met10010100.
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The potential of ultrasonic surface mechanical attrition treatment (SMAT) at different temperatures (including cryogenic) for improving the fatigue performance of 304L austenitic stainless steel is evaluated along with the effect of the fatigue loading conditions. Processing parameters such as the vibration amplitude, the size, and the material of the shot medias were fixed. Treatments of 20 min at room temperature and cryogenic temperature were compared to the untreated material by performing rotating–bending fatigue tests at 10 Hz. The fatigue limit was increased by approximately 30% for both peening temperatures. Meanwhile, samples treated for 60 min at room temperature were compared to the initial state in uniaxial fatigue tests performed at R = −1 (fully reversed tension–compression) at 10 Hz, and the fatigue limit enhancement was approximately 20%. In addition, the temperature measurements done during the tests revealed a negligible self-heating (∆t < 50 °C) of the run-out specimens, whereas, at high stress amplitudes, temperature changes as high as 300 °C were measured. SMAT was able to increase the stress range for which no significant local self-heating was reported on the surface.
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Khosravi, Aliakbar, Tuck Wai Yeong, Mohammed Parvez Anwar, Jayaprakash Jaganathana, Teck Leong Lau, and Wael Elleithy. "A Comparative Study between Three-Legged and Tripod Sub-structures in Design of Offshore Wind Turbines in the Transition Water Depth." International Journal of Engineering & Technology 7, no. 3.36 (May 6, 2018): 23. http://dx.doi.org/10.14419/ijet.v7i3.36.29073.
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This research aimed at investigating tripod and three-legged offshore wind turbine substructures. A comparison between the two substructures based on their weight as well as the installation method of piles, i.e. pre-piling and post-piling, was carried out. The in-place (Ultimate Limit State), Dynamic, natural frequency check and fatigue (Fatigue Limit State) analyses were conducted considering aerodynamic and hydrodynamic loads imposed on substructures in 50m water depth. An optimisation process was carried out in order to reduce the mass of substructures. The results revealed that the three-legged substructure is more cost effective with 25% lesser structure mass. However, the construction of the three-legged structure usually takes more time due to increased number of members and subsequently welding joints. The results, furthermore, showed that the pre-piling method reduces the time and cost of offshore installation, and reduces the weight of piles by 50%.
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Sigurdsson, G., and R. Torhaug. "Discussion of the Fatigue Crack Model Used as Decision Basis for Probabilistic Inspection Planning." Journal of Offshore Mechanics and Arctic Engineering 117, no. 2 (May 1, 1995): 137–44. http://dx.doi.org/10.1115/1.2827064.
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Marine structures are often highly utilized structures and are operating in an environment dominated by dynamic loading. The fatigue limit state is of main concern and is governing the structural dimensions and the amount of resources utilized in inspection of several members and joints. There is a considerable uncertainty related to the parameters determining the fatigue life, and probabilistic analyses have therefore been used extensively in fatigue analysis. The models used both on describing the fatigue driving mechanisms and the deterioration mechanism, however, are always compromises between ability to describe nature and computational applicapability. In a state-of-the-art probabilistic fatigue analysis, major assumptions are made when establishing the crack growth model, such as: 1) the relation between membrane and bending stresses is assumed to be constant for all stress ranges, and one common stress component for the total stress is used to calculate fatigue crack growth. 2) The crack growth is assumed to follow a pattern with a constant relation between crack depth and crack length. This paper investigates the foregoing fundamental assumptions for the fatigue driving mechanism and shows the effect on time to the first inspection based on state-of-the-art probabilistic crack growth analysis for the detail of interest, for a simple but realistic jacket structure.
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Chai, Y. H., and K. M. Romstad. "Correlation between Strain-Based Low-Cycle Fatigue and Energy-Based Linear Damage Models." Earthquake Spectra 13, no. 2 (May 1997): 191–209. http://dx.doi.org/10.1193/1.1585941.
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Although the potential for cumulative damage of structures during long duration earthquakes is generally recognized, most design codes do not explicitly takes into account the damage potential of such events. In this paper, a strain-based low-cycle fatigue model commonly used for the prediction of fatigue life in metals is adapted for cumulative damage assessment of structures under seismic conditions. By defining the number of load cycles in terms of the total plastic strain energy dissipated by the structure, the model is presented in a form capable of predicting the plastic strain energy capacity of the structure at the ultimate limit state. The plastic strain energy is expected to decrease rapidly with increased displacement in the small displacement range and to decrease gradually in a near linear manner with increased displacement in the large displacement range. The model is shown to calibrate reasonably well with small-scale aluminum cantilever specimens tested under large-amplitude reversed cyclic loading. At the ultimate limit state, the modified Park and Ang damage model may be considered as a linear approximation to the low-cycle fatigue model in the large displacement range.
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Andersen, Jacob, Rune Abrahamsen, Thomas Andersen, Morten Andersen, Torben Baun, and Jesper Neubauer. "Wave Load Mitigation by Perforation of Monopiles." Journal of Marine Science and Engineering 8, no. 5 (May 16, 2020): 352. http://dx.doi.org/10.3390/jmse8050352.
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The design of large diameter monopiles (8–10 m) at intermediate to deep waters is largely driven by the fatigue limit state and mainly due to wave loads. The scope of the present paper is to assess the mitigation of wave loads on a monopile by perforation of the shell. The perforation design consists of elliptical holes in the vicinity of the splash zone. Wave loads are estimated for both regular and irregular waves through physical model tests in a wave flume. The test matrix includes waves with Keulegan–Carpenter ( K C ) numbers in the range 0.25 to 10 and covers both fatigue and ultimate limit states. Load reductions in the order of 6%–20% are found for K C numbers above 1.5. Significantly higher load reductions are found for K C numbers less than 1.5 and thus the potential to reduce fatigue wave loads has been demonstrated.
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Bao, Ke, Qiu Fang Wang, Shu Lin Liu, and Zhong Liang Wei. "Study on Local Strain Field Intensity Approach for Prediction Fatigue Life of Crankshaft Based on Mechanical Mechanics." Advanced Materials Research 644 (January 2013): 251–55. http://dx.doi.org/10.4028/www.scientific.net/amr.644.251.
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The bending fatigue limit moment and crack initiation life of 4105 crankishaft in five groups of bending moments are obtained by resonant bending fatigue tests first. Then, the static finite element calculation using sub-model is performed to get the strain distributions in every test load. The results show that in the region where stress concentrate, the strain field could be seen as plane strain state. So two dimensional strain field intensity model is selected. In order to remove the influences of size and surface conditions, the radius of strain field is determined with the strain distribution under the low-life test load. After that, the local strain field intensities under each test load are calculated with the radius of strain field. Finally, the strain-life curve of material is modified by the fatigue intensity limit of crankshaft, and the predicted life agree with the test results.
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Kirkegaard, P. H., I. Enevoldsen, J. D. So̸rensen, and R. Brincker. "Reliability Analysis of a Mono-Tower Platform." Journal of Offshore Mechanics and Arctic Engineering 112, no. 3 (August 1, 1990): 237–43. http://dx.doi.org/10.1115/1.2919862.
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In this paper, a reliability analysis of a Mono-tower platform is presented. The failure modes considered are yielding in the tube cross sections and fatigue failure in the butt welds. The fatigue failure mode is investigated with a fatigue model, where the fatigue strength is expressed through SN relations. In determining the cumulative fatigue damage, Palmgren-Miner’s rule is applied. Element reliability, as well as systems reliability, is estimated using first-order reliability methods (FORM). The sensitivity of the systems reliability to various parameters is investigated. It is shown that the fatigue limit state is a significant failure mode for the Mono-tower platform. Further, it is shown for the fatigue failure mode that the largest contributions to the overall uncertainty are due to the damping ratio, the inertia coefficient, the stress concentration factor, the model uncertainties, and the parameters describing the fatigue strength.
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Lee, Young-Joo, and Wonho Suh. "Risk and sensitivity quantification of fracture failure employing cohesive zone elements." Advances in Mechanical Engineering 11, no. 9 (September 2019): 168781401987831. http://dx.doi.org/10.1177/1687814019878319.
Full textAbstract:
Many structures are subjected to the risk of fatigue failure. For their reliability-based design, it is thus important to calculate the probability of fatigue failure and assess the relative importance of the involved parameters. Although various studies have analyzed the fatigue failure, the stage of fracture failure has been less focused. In particular, the risk analysis of fracture failure needs to be conducted considering its importance in actual structures. This article proposes a new probabilistic framework for the risk and sensitivity analysis of structural fatigue failure employing cohesive zone elements. The proposed framework comprises three steps, namely finite element analysis using cohesive zone elements, response surface construction, and risk and sensitivity analysis of fatigue failure, which require several mathematical techniques and algorithms. The proposed framework is tested by applying it to an illustrative example, and the corresponding analysis results of fracture failure probability with different threshold values of a limit-state function are presented. In addition, the sensitivities of failure risk with respect to the statistical parameters of random variables are presented and their relative importance is discussed.
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Weingärtner, Regina, Jürgen Hoffmeister, and Volker Schulze. "Generation and Determination of Compressive Residual Stresses of Short Penetration Depths." Materials Science Forum 768-769 (September 2013): 580–86. http://dx.doi.org/10.4028/www.scientific.net/msf.768-769.580.
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Generating compressive residual stress states with high gradients and low penetration depths offers high capability regarding increase of fatigue limit of parts. In this work the determination of such specific residual stress distributions by using X-ray diffraction and a little material removal is introduced. Measurements are compared using two interference peaks of different penetration depths, at which confocal microscopy enables high accuracy in determination of the step sizes in electrochemical machining. Furthermore the realisation of these states by two different peening processes using micro blasting media is described. The suitability of the processes micro peening and ultrasonic wet peening as surface treatment methods to improve fatigue limit are shown. Micro peening is based on the shot peening principle with small shots and ultrasonic wet peening on the acceleration of small blasting particles by cavitation. The investigations were conducted at AISI 4140 in a quenched and tempered state. Besides the residual stresses and the integral width of interference peaks as well as the depth distributions, the surface topography was examined. The beneficial effects of these conditions on the fatigue limit in bending tests are described.
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Vázquez, J., A. Silvera, F. Arias, and E. Soria. "Fatigue properties of a glass-fibre-reinforced polyester material used in wind turbine blades." Journal of Strain Analysis for Engineering Design 33, no. 3 (April 1, 1998): 183–93. http://dx.doi.org/10.1243/0309324981512904.
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Glass-fibre-reinforced polyester (GFRP) is a composite commonly used in the manufacture of wind turbine blades. In the present work, one such material has been subject to static and dynamic tests in order to obtain data that can be applied to the design of wind turbine blades and other machine elements. The results of the static tests established a basis for the determination of a set of tension-tension (constant amplitude and sinusoidal load) dynamic tests with the aim of establishing a mathematical model in order to predict life as a function of the load state and calculate the fatigue limit. The multiplicative model (y = axb) for y = log of life and x = transformed stress (a and b are characteristic parameters of the material obtained from data) matches the data quite well. The conclusion is that the GFRP studied has no fatigue limit. The possible decrease of fatigue strength of the material with solar radiation and moisture absorption was also investigated, with a negative result.
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Ramirez, Guillermo, Paul H. Ziehl, and Timothy J. Fowler. "Nondestructive Evaluation of FRP Design Criteria With Primary Consideration to Fatigue Loading." Journal of Pressure Vessel Technology 126, no. 2 (May 1, 2004): 216–28. http://dx.doi.org/10.1115/1.1688371.
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Design of FRP tanks and pressure vessels is based on criteria developed in the late 1960s using materials and procedures that represented the state of the art at the time. Maximum strain has been the controlling factor selected for the design of these vessels at an allowable level of 0.001. With the development of newer materials and systems with recorded performances of better than 0.001 this is now an inefficient limit in the design. Tests performed in the programs described in this paper indicate that newer materials perform well at higher strains. Results of strength tests performed here indicated that strains of 0.002 to 0.003 or better are possible in the safe design of tanks and pressure vessels. In addition, more accurate determination of design limits is possible if methods like acoustic emission are incorporated in the design process.
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Bakuckas, J. G., W. S. Johnson, and C. A. Bigelow. "Fatigue Damage in Cross-Ply Titanium Metal Matrix Composites Containing Center Holes." Journal of Engineering Materials and Technology 115, no. 4 (October 1, 1993): 404–10. http://dx.doi.org/10.1115/1.2904238.
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The development of fatigue damage in four [0/90]s SCS-6/Ti-15-3 laminates containing center holes was investigated. A methodology to predict damage initiation based on an effective strain parameter was used to determine the stress levels and the number of cycles required for matrix crack initiation. Damage progression was monitored at various stages of fatigue loading. In general, a saturated state of damage consisting of matrix cracks and fiber-matrix debonding was obtained which reduced the composite modulus. Matrix cracks were bridged by the 0° fibers. The fatigue limit (stress causing catastrophic fracture of the laminates) was also determined. The static and post-fatigue residual strengths were accurately predicted using a three dimensional elastic-plastic finite element analysis. The matrix damage that occurred during fatigue loading significantly reduced the notched strength.
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Fintová, Stanislava, Libor Pantělejev, and Ludvík Kunz. "Microstructure and Mechanical Properties of Ultrafine-Grained Magnesium AZ91 Alloy." Materials Science Forum 782 (April 2014): 384–89. http://dx.doi.org/10.4028/www.scientific.net/msf.782.384.
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Microstructure, mechanical properties, cyclic plastic deformation behavior and fatigue strength of ultrafine-grained (UFG) magnesium alloy AZ91 processed by equal channel angular pressing (ECAP) were investigated. ECAP of originally cast alloy results in development of bimodal structure, improved yield stress, tensile strength and ductility when compared to the as-cast state. Endurance limit based on 107cycles is also improved, however exhibits large scatter. Initiation of fatigue cracks takes place in regions of large grains in the bimodal structure, where the content of Mg17Al12particles is low.
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Savelyev, Artem. "Compensatory-adaptive mechanism of cardiorespiratory system in athletes’ fatigue state." Tambov University Review. Series: Humanities, no. 179 (2019): 98–104. http://dx.doi.org/10.20310/1810-0201-2019-24-179-98-104.
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At the present level of sports development, the search for opportunities to improve the performance and endurance of athletes is one of the most important terms for achieving high sports results. Performing physical activity at the limit level makes increased demands on the ac-tivity of the body, requires more significant adaptive changes in the functioning of all organs and systems, but it allows to raise the overall level of efficiency. Factors that determine the effective-ness of combinations of training loads are the volume of loads, their direction and sequence of ex-ecution. Consideration of these factors should be reflected in the organization of the training process. The combination of training loads aimed at the education of general, special and strength endurance should be most often used in the general preparatory stage of the preparatory period, and the combination of loads aimed at the education of special, speed and strength endurance – in the special preparatory stage of the preparatory period and in the competitive period. Planning the volume and intensity of the training load and its implementation should correspond to the functional capabilities of the athlete’s body. To prevent the probability of any deviation from normal functioning of energy sustaining systems of the body, one needs a speedy and effective recovery of these systems. Only in this case the training process can proceed quite systematically, and the results of the trainee will become more stable at all stages of the competition period. All this makes it relevant to study the processes of rational interaction of cardiorespiratory and motor systems of the body during training and competition. This knowledge allows with a sufficient degree of accuracy to determine the development of the performance of athletes, optimize the training process, improve its quality and efficiency, maintain a high level of performance for a long time.
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Jiao, Sheng Bo, Li Cheng, Quan Tong Li, and Xiao Wei Li. "Study on Very-High-Cycle-Fatigue Property of Aero-Engine Blades Based on Subcomponent Specimen." Key Engineering Materials 664 (September 2015): 87–95. http://dx.doi.org/10.4028/www.scientific.net/kem.664.87.
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The cyclic load number of aero-engine blade during its service life is very likely beyond 107, which is regarded as the conventional fatigue limit. Moreover, surface strengthening is very often used in the manufacturing process of blade. The conventional testing method in the VHCF regime cannot exactly reflect the stress state of the blade, including the mechanism of crack initiation. To study the fatigue behavior and effects of laser shock peening, a kind of bending fatigue subcomponent specimen was designed and the laser shock peening model was established. Experiment about TC17 was accomplished by the Ulra-High Cycle bending fatigue system. It is found that the fatigue damage occurs beneath the surface and the S-N curve is continuously rather than multi-step declining in the VHCF regime. Process of surface strengthening has a significant effect on fatigue performance of TC17 titanium alloy.
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Castro, Oscar, Kim Branner, and Nikolay Dimitrov. "Assessment and propagation of mechanical property uncertainties in fatigue life prediction of composite laminates." Journal of Composite Materials 52, no. 24 (March 22, 2018): 3381–98. http://dx.doi.org/10.1177/0021998318765626.
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A probabilistic model for estimating the fatigue life of laminated composite materials considering the uncertainty in their mechanical properties is developed. The uncertainty in the material properties is determined from fatigue coupon tests. Based on this uncertainty, probabilistic constant life diagrams are developed which can efficiently estimate probabilistic ɛ-N curves at any load level and stress ratio. The probabilistic ɛ-N curve information is used in a reliability analysis for fatigue limit state proposed for estimating the probability of failure of composite laminates under variable amplitude loading cycles. Fatigue life predictions of unidirectional and multi-directional glass/epoxy laminates are carried out to validate the proposed model against experimental data. The probabilistic fatigue behavior of laminates is analyzed under constant amplitude loading conditions as well as under both repeated block tests and spectral fatigue using the WISPER, WISPERX, and NEW WISPER load sequences for wind turbine blades.
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Jambor, Michal, Libor Trško, Jan Klusák, Stanislava Fintová, Daniel Kajánek, František Nový, and Otakar Bokůvka. "Effect of Severe Shot Peening on the Very-High Cycle Notch Fatigue of an AW 7075 Alloy." Metals 10, no. 9 (September 18, 2020): 1262. http://dx.doi.org/10.3390/met10091262.
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The severe shot peening process was applied to the notched specimens from an AW 7075 alloy with the aim to improve fatigue endurance in the very-high cycle fatigue region. To reveal the stress state in the notch vicinity, finite element analysis was performed, simulating the conditions of the used 20 kHz ultrasonic fatigue loading. Modified surface characteristics by the severe shot peening process were analyzed in terms of residual stress distribution measured by X-ray diffraction methods and near-surface microstructural observations by scanning electron microscopy. The applied severe shot peening increased the fatigue limit by 11%; however, the positive effect was recorded only for the loading amplitudes corresponding to the fatigue lifetimes in the range 107–109 cycles. At higher loading amplitudes, the fatigue properties tended to decrease, most likely due to accelerated fatigue crack initiation on the surface damage features created by the peening process and also by rapid residual stress relaxation.
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Radlbeck, Christina, Mathias Rengstl, Senta Pessel, and Martin Mensinger. "(Low-Cycle-) Fatigue Design According to DIN EN 1999-1-3 State of the Art and Current Research." Key Engineering Materials 710 (September 2016): 439–44. http://dx.doi.org/10.4028/www.scientific.net/kem.710.439.
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DIN EN 1999-1-3 presents a comprehensive framework for fatigue design of aluminum structures. Various structural details and joints are included. For safety checks against High-Cycle Fatigue, three design concepts are available: Safe-Life-Design, Damage-Tolerant-Design and Design assisted by Testing. Respective safe-life-design lines are based on a databank including results from stress controlled Wöhler fatigue tests. The phenomenon of Low-Cycle-Fatigue (<105 cycles) is treated in Annex F, giving design regulations for selected structural details. Thereby, the influence of different alloys and thus different yield strength values is not considered. In addition, plasticizing effects under high stress ranges are neglected. In general, engineers face the following questions: Which cycle numbers require (Low-Cycle-) fatigue design and thus where is the limit for static design? Furthermore, how to define the maximum allowable stress range? Respective answers are investigated in a current research project carried out by the Chair of Metal Structures, TU Munich.In this contribution, the state of the art of fatigue design according to DIN EN 1999-1-3 is presented. European design concepts are discussed in view of available data and new developments in research, quality control, fabrication of specimen as well as testing techniques. The focus is then laid on Low-Cycle Fatigue. A new concept, including the influence of alloy type and the effects of plasticizing, is worked on. To this purpose an extensive testing program has started, including a large number of strain-controlled-tests.
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Sun, YuanTao, Chao Liu, Qing Zhang, and XianRong Qin. "Multiple Failure Modes Reliability Modeling and Analysis in Crack Growth Life Based on JC Method." Mathematical Problems in Engineering 2017 (2017): 1–5. http://dx.doi.org/10.1155/2017/2068620.
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The fatigue crack growth (FCG) phenomenon generally exists in large mechanical structures. Due to the influences of varied kinds of random factors, the safety evaluation of structure in FCG is under great uncertainty. In this paper, based on the reliability theory, the limit state equations of fracture failure and static strength failure were derived firstly, and the parameters in those equations were regarded as random variables that follow the normal distribution or log-normal distribution. According to the limit state equations, the JC method (equivalent normalizing method) was used to calculate the reliability indexes under the different failure modes of structure in every stress cycle. Based on the reliability indexes and correlation of the two failure modes, the joint failure probability was obtained. In the end, a specific computation example was given, and the curve of joint failure probability in multiple failure modes was used for comparison with the result of single failure mode. The results indicated that the reliability analysis based on multiple failure modes was more reasonable, and the evaluation of reliability could be obtained in fatigue crack growth process.
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Ruffing, Christoph, and Eberhard Kerscher. "Fatigue Behavior of Ultrafine Grained Medium Carbon Steel with Different Carbide Morphologies Processed by High Pressure Torsion ." Advanced Materials Research 891-892 (March 2014): 428–33. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.428.
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The increased attention that ultrafine grained (UFG) materials have received over the last decade has been provoked, not least, by their high strength in combination with remarkable ductility. The main focus of our investigation was the evaluation of the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steel. In our case HPT increased the hardness by a factor of 1.75 - 3.2 compared to the initial states. The achieved hardness maximum was 726 HV. The amount of increase depended on the initial carbide morphology. By stress controlled cyclic four point bending tests with a load ratio of 0.1 endurance limits were determined for the initial and HPT states. The endurance limit increased linearly with hardness until 500 HV and independently of the carbide morphology. All fracture surfaces were investigated by SEM after the fatigue tests. They revealed pretty flat fatigue fracture surfaces with crack initiation at the surface or rather at non-metallic inclusions for the UFG states. Morphology and crack initiation mechanisms were changed by severe plastic deformation compared with the coarse grained initial state. Residual fracture surfaces with a spheroidal initial microstructure showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with initial tempered microstructure showed rather brittle and rough residual fracture surfaces.
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Liu, Fang, Ming Xie, Yanjun Ji, and Mengzhen Zhou. "Progressive fatigue damage analysis of composite bolted joint using equivalent stress model." Science Progress 103, no. 1 (September 16, 2019): 003685041987423. http://dx.doi.org/10.1177/0036850419874234.
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Composite bolted joints are quite necessary for composite structures connection, which has become the main limit for the use of composites in main load-bearing structures. In this article, a fatigue model of composite bolted joint based on equivalent stress is established by programming in ABAQUS USDFLD subroutine to simulate the progressive failure of composite bolted joints. By introducing three-dimensional Tsai–Hill static failure criterion, equivalent stress is calculated for investigating effects of multiaxial stress on fatigue life. In the subroutine of progressive failure for fatigue model, fatigue life of composite bolted joint and damage state of elements that are meshed in the process of modelling are connected by defining field variable. Different fatigue modes are predicted here by changing stress amplitude and ratio loading, in which simulation results agree well with that obtained in corresponding experiments.
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Yang, You, and Wei Feng Tang. "Study on Fatigue Behaviors of 0Cr21Mn17Mo2N0.83 High Nitrogen Stainless Steels." Key Engineering Materials 861 (September 2020): 89–94. http://dx.doi.org/10.4028/www.scientific.net/kem.861.89.
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High cycle fatigue behaviors of 0Cr21Mn17Mo2N0.83 high nitrogen stainless steels at forged and solid solution state were investigated. High cycle fatigue tests were carried out up to 107cycles at a stress ratio R=0.1 and frequency of 70Hz on specimens using a high frequency fatigue machine. Fatigue fracture surfaces of specimens that in the high cycle fatigue tests were observed using a scanning electron microscope for revealing the micro-mechanisms of fatigue crack initiation and propagation. The results showed that the fatigue limit of test alloys at room temperature is 865.25 MPa (as-forged alloy) and 736.10MPa (solid solution alloy), respectively. The micro-fatigue fracture surface of the test alloys included three representative regions. These regions are fatigue initiation area, fatigue crack propagation area and fatigue fracture area. Fatigue cracks of the test alloys initiate principally at the precipitates, inclusion or uneven stress concentration sites of alloy surface, and propagate along the grain boundary. The fatigue striations of fatigue crack propagation area are very clear. The fatigue fracture of test specimens show the rupture characteristics of quasi cleavage and dimple fracture. The room temperature fatigue properties of as-forged alloy are generally higher than that of the solid solution high nitrogen stainless steel according to the S-N curves fitting results.
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Xing, Zhiguo, Zhiyuan Wang, Haidou Wang, and Debin Shan. "Bending Fatigue Behaviors Analysis and Fatigue Life Prediction of 20Cr2Ni4 Gear Steel with Different Stress Concentrations near Non-metallic Inclusions." Materials 12, no. 20 (October 21, 2019): 3443. http://dx.doi.org/10.3390/ma12203443.
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To investigate the relationship between inclusions and bending fatigue behaviors in 20Cr2Ni4 steel under different stress concentrations. This paper designs a new experimental method to prefabricate different size stress concentrations near the inclusions, and then conducts a new type of bending fatigue test to study the inclusions and their surrounding stress distributions in 20Cr2Ni4 steel. A microhardness tester was combined with laser etching equipment to realize the prefabrication of different stress concentrations at arbitrary positions around any inclusion on the gear steel surface. This method provides an experimental basis for the quantitative analysis of the relationship between stress distribution and fatigue life around the inclusions of heavy-duty gear steels. We also predict the bending fatigue lives of heavy-duty gear steels with different types of inclusions, stress states, and spatial distributions. Then, based on the prefabricated notch parameters and the state of inclusions in the steel, a mathematical model of quantitative analysis is proposed, which can accurately predict the fatigue limit of heavy-duty gear steel. The research results can be applied to the actual use of heavy-duty gears and to the accurate life estimation based on the state of gear stress, thereby providing a quantitative reference model for subsequent gear steel production and gear part processing.
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Subramonian*, Kavyashree, and Sumathi, G. "Drowsiness Detection System with Speed Limit Recommendation using Sentiment Analysis." International Journal of Recent Technology and Engineering 10, no. 1 (May 30, 2021): 184–90. http://dx.doi.org/10.35940/ijrte.a5848.0510121.
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Driving while drowsy is a ubiquitous and extremely grave public health hazard that requires immediate consideration. Through studies in recent years, it has been proved that about 20 percent of all car accidents have occurred as a result of dozy driving. The main objective of new drowsiness detection systems is accurate doziness recognition. In this regard, the face is the most important part of the body as it sends a lot of essential information. The facial expressions of a drowsy driver include frequency of blinking and yawning. This paper proposes a model which detects the drivers' awareness using video stills of the driver’s face and improves the tracking accuracy. Further, we introduce the auxiliary functionality of speed limit recommendations based on the driver’s present state of mind. The various facial features are evaluated to determine the drivers' current state. By combining the features of the eyes and mouth, the driver is alerted with a fatigue warning and also suggested a safe speed limit. This system is very essential so as to prevent and hence reduce the number of fatal accidents that occur as a result of dozy driving saving a lot of lives and damage to property.