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1
Artym, V. I., O. Y. Faflei, V. F. Pents und A. M. Kariuk. „FEATURES OF DURABILITY CALCULATION FOR MACHINE PARTS AND STRUCTURAL ELEMENTS UNDER HIGH ASYMMETRIC LOW-AMPLITUDE LOAD CONDITIONS“. ACADEMIC JOURNAL Series: Industrial Machine Building, Civil Engineering 1, Nr. 50 (11.04.2018): 14–24. http://dx.doi.org/10.26906/znp.2018.50.1090.
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The study has been conducted by means of physical, mathematical and computer modeling integrated method use. To prove the adequacy of the results obtained the experimental procedure on the existing equipment and laboratory facilities has been applied. The method of carrying out asymmetric stress cycles with mean stress of stretching to symmetric using the proposed piecewise – linear equations for evaluating the material sensitivity to asymmetry of the cycle has also been improved. It has enabled pipe column element durability under the condition of typical asymmetric low-amplitude loading calculation.
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Vĕchet, Stanislav, Jan Kohout, Klára Hanzlíková und Vojtěch Hruby. „The Influence of Mean Stress on Fatigue Properties of ADI“. Materials Science Forum 567-568 (Dezember 2007): 341–44. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.341.
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The paper presents the results of research focused on assessment of the influence of loading cycle asymmetry on fatigue limit values. For tests two heats of unalloyed nodular cast iron were used. Test bars made of keel blocks were heat treated in salt bathes (austenitization at 900 °C during 1 hour, isothermal transformation at 380 and 400 °C) and loaded at symmetrical, repeating and pulsating loading cycles at room temperature. Evaluation of fatigue properties was based on the determination of S-N curves in high-cycle region including the fatigue limit assessment for 107 cycles to fracture. Fatigue and static tests were completed by metallographic and quantitative phase analysis. Most important result obtained from the presented study is that the dependence of stress amplitude on mean stress cannot be approached by the linear relation but by general power law with exponent lower than 1 (i.e. the Haigh diagram has convex shape).
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Nový, František, Juraj Belan und Otakar Bokůvka. „Safety of Construction Components in a Very High Number of Load Cycles“. System Safety: Human - Technical Facility - Environment 2, Nr. 1 (01.03.2020): 199–206. http://dx.doi.org/10.2478/czoto-2020-0024.
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AbstractProgressive, high-strength materials have an important position in the transport industry. In this industry, components are subject to high safety and reliability requirements because they often operate under long-term cyclic stress regimes. The paper presents results of fatigue resistance of high-strength materials such DOMEX 700MC, HARDOX 400, HARDOX 450, and INCONEL 718 (UTS from 850 to 1560 MPa) measured at high-frequency cyclic loading (f = 20 kHz, T = 20 ± 5 ° C, push-pull loading, cycle asymmetry parameter of R = -1) in the area from N = 2x106 to N = 2x108 cycles. Fatigue resistance showed a continuous decrease about average value Sa 2x108/Sa 2x106 = 19.1%.
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Viet, Nguyen Van, Wael Zaki und Ziad Moumni. „A model for shape memory alloy beams accounting for tensile compressive asymmetry“. Journal of Intelligent Material Systems and Structures 30, Nr. 18-19 (22.09.2019): 2697–715. http://dx.doi.org/10.1177/1045389x19873407.
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A new analytical model is derived for cantilever beams made from superelastic shape memory alloy and subjected to tip load. The deformation of the beam is described based on Timoshenko beam theory using constitutive relations that account for asymmetric shape memory alloy response in tension and compression. Analytical moment and shear force equations are developed and the position of the neutral axis and the different solid phase regions in the beam are tracked throughout a full loading–unloading cycle. Validation of the proposed model is carried out against data from the literature and from the finite element analysis considering tensile–compressive asymmetry in shape memory alloy behavior.
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Chen, Yan Hua, und Qing Jie Zhu. „Numerical Simulation of Interfacial Bonding Degradation of Composites under Two-Stage Loading“. Materials Science Forum 575-578 (April 2008): 869–74. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.869.
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Bonding degradation at interface is one of main damage forms of composites, especially under fatigue loading. Interfacial bonding degradation of FRC under two-stage tension loading is studied, which is base for variable-amplitude cyclic loading existing widely in actual engineering. Based on the shear-lag model and considered the asymmetry of interfacial damage, the mechanical governing equations of fiber and matrix are established and related solutions are obtained firstly. Two kinds of loading models are chosen, one is low-high alternate loading, and the other is low early and high late loading. By the aid of the Paris law and the energy release theory, a relationship between debond rate and cycle number is established. Then the interfacial debonding is simulated under the two-stage tension loading. The rules of the crack growth are analyzed for low-high two-stage loadings. It is found that stress amplitude has great influence on interfacial debonding under two-stage loading. Low stress amplitude in a certain range can postpone interfacial bonding degradation. And interfacial damage extent is greater than that under constant-amplitude fatigue loading. Present study is helpful for analyzing the fatigue damage of engineering materials and structures.
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Rubtsov, Igor, Ramidin Alisultanov, Alexander Zinatullin und Nikolay Midrigan. „Detection of fatigue damage in long-span reinforced concrete structures“. MATEC Web of Conferences 196 (2018): 03010. http://dx.doi.org/10.1051/matecconf/201819603010.
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The emergency situations and catastrophes with buildings and structures may be caused by both the short-time loads considerably exceeding the design load values and the cyclic loads exciting the fatigue damage in the structure material. The cyclic influence is characterized by the amplitude, the cycle asymmetry and the number of loading cycles. To reveal all the factors of a cyclic influence is possible by the on-line measurement of stresses or that of strains at the structure under observation.
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Yu Solovyov, L., und A. L. Solovyov. „The effect of asymmetry of the loading cycle on heat dissipation in metal structures“. IOP Conference Series: Materials Science and Engineering 760 (07.02.2020): 012055. http://dx.doi.org/10.1088/1757-899x/760/1/012055.
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8
Jambor, Michal, František Nový, Otakar Bokůvka, Libor Trško und Monika Oravcová. „Influence of structure sensitising of the AlSi 316Ti austenitic stainless steel on the ultra-high cycle fatigue properties“. MATEC Web of Conferences 157 (2018): 05011. http://dx.doi.org/10.1051/matecconf/201815705011.
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Austenitic stainless steels are the wide-spread materials, used mainly in the power industry. In that kind of engineering application, structural parts of rotating elements reach during their lifetime very high numbers of loading cycles, exceeding 107 numbers of cycles. With regard to this fact, the data of ultra-high cycle fatigue properties are needed to be used in the qualified design. Increasing demands on the efficiency cause the increase of the operating temperature, and exposition of these materials to the elevated temperatures can cause some important structural changes, which result in the sensitising of the structure. In this study authors present their own experimental results about fatigue properties of AISI 316Ti austenitic stainless steel after sensitising, in the ultra-high cycle region (Nf = 106 ~ Nf = 3×109 cycles). Fatigue tests were carried out using ultrasonic fatigue testing device with frequency f = 20 kHz at the coefficient of cycle asymmetry R = -1, and temperature T = 20±5°C. In the ultra-high cycle region was observed the continuous decrease of the fatigue properties of the AISI 316Ti, and there was recorded the negative effect of the sensitising on the ultra-high cycle fatigue properties of the AISI 316Ti.
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Roşca, Valcu, und Cosmin Mihai Miriţoiu. „The NASGRO Method - Comparison Model for the Crack Growth Rate Calculus“. Applied Mechanics and Materials 880 (März 2018): 53–62. http://dx.doi.org/10.4028/www.scientific.net/amm.880.53.
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The products materials failure process subjected to a time variable loading can be watched and controlled through the study of an important parameter from the “Fracture Mechanics” given by the crack growth rate or the cracking rate. This is marked with da/dN, sometimes da/dt, representing the length variation a at a fatigue loading cycle. From the most used models for its study, one can remember: methods that use the American standards ASTM, Paris formula model or the Walker one. The model called NASGRO or FNK is used to study the crack growth evolution in NASA studies, being a more complex method, for the cracking process. The results obtained were compared to the ones determined with the above methods. For the tests, steel samples R520 were used, CT type, with side notch. The loading cycle was made with the asymmetry coefficient R= 0.5, at the temperatures: 293K, 252K and 213K.
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Kofto, D. G. „Effect of loading frequency and cycle asymmetry on the fatigue resistance of alloy AMg, 6N“. Strength of Materials 22, Nr. 2 (Februar 1990): 283–89. http://dx.doi.org/10.1007/bf00773252.
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11
Savkin, A. N., K. A. Badikov und A. A. Sedov. „Modeling and calculation of the fatigue crack growth life in structural steels“. Industrial laboratory. Diagnostics of materials 87, Nr. 4 (23.04.2021): 43–51. http://dx.doi.org/10.26896/1028-6861-2021-87-4-43-51.
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The kinetics of fatigue crack growth has been studied in tensile testing of compact steel tensile specimens (S(T)-type) in the middle section of the kinetic diagram of fatigue fracture (fatigue crack growth diagram) under regular and irregular loading with different asymmetry and maximum load values. The samples were tested on a BISS Nano-25kN servo-hydraulic machine. Standard loading spectra typical for different technical objects exposed to alternating loading during operation were used. The values of the crack growth rate per cycle in the loading block were obtained. Parameters for assessing the character of irregular loading and crack closure, namely, the irregularity factor and crack closure coefficient were proposed. When calculating the effective value of the range of the stress intensity factor (SIF) at the crack mouth, we propose also to take into account the loading irregularity in addition to the closure coefficient. With this approach, the obtained fatigue crack growth diagrams can be grouped into one equivalent curve, which is characteristic of regular loading with R = 0. Moreover, grouping of the fatigue crack growth diagrams provided the use of unified parameters when calculating the crack growth kinetics, regardless of the type and parameters of loading, which rather simplified the crack growth determination. The fatigue crack growth life was predicted taking into account the crack «closure» and the nature of loading according both to the approach developed by the authors and by cyclic calculation method (cycle-by-cycle). All the data obtained are tabulated and classed according to the type of loading. The calculation results and experimental data showed good convergence, which was confirmed by the high values of the correlation coefficient.
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Vetrov, A. N., und V. I. Molodkin. „Effect of loading asymmetry on the low-cycle fatigue of ZhS6F alloy in cyclic temperature variations“. Strength of Materials 20, Nr. 8 (August 1988): 1034–40. http://dx.doi.org/10.1007/bf01528675.
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13
Pokrovskii, V. V., V. G. Kaplunenko, Yu I. Zvezdin und B. T. Timofeev. „Effect of the loading cycle asymmetry on the cyclic cracking resistance characteristics of heat-resisting steels“. Strength of Materials 19, Nr. 11 (November 1987): 1473–78. http://dx.doi.org/10.1007/bf01523026.
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14
Belodedenko, S. V., G. N. Bilichenko und D. E. Kozakov. „Accumulation of fatigue damage and lifetime prediction under irregular loading conditions with overloads and random cycle asymmetry“. Strength of Materials 29, Nr. 2 (März 1997): 137–41. http://dx.doi.org/10.1007/bf02767589.
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15
Dragan, V. I., S. M. Semenyuk, E. I. Mitchenko und V. O. Merkulov. „Effect of loading cycle asymmetry, stress concentration, and fretting corrosion on the fatigue resistance of alloy D16T“. Strength of Materials 22, Nr. 5 (Mai 1990): 678–84. http://dx.doi.org/10.1007/bf00806268.
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16
Ostash, O. P., V. T. Zhmur-Klimenko, E. M. Kostyk und A. B. Kunovskii. „Influence of crack closure and loading cycle asymmetry on kinetic fatigue failure curves at normal and low temperatures“. Soviet Materials Science 23, Nr. 3 (1987): 285–89. http://dx.doi.org/10.1007/bf00720890.
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17
C., Kwang T., Mohd Luqman Mohd Jamil und Auzani Jidin. „Torque improvement of PM motor with semi-cycle stator design using 2D-finite element analysis“. International Journal of Electrical and Computer Engineering (IJECE) 9, Nr. 6 (01.12.2019): 5060. http://dx.doi.org/10.11591/ijece.v9i6.pp5060-5067.
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This paper presents sizing approaches to improve output torque performance in PM motor when partial stator body is removed. As the output torque performance is directly proportional to the electric loading, Q, modification on stator geometry affects the output torque performance and special procedures have to be taken to restore the desired output torque capability. Influences of split ratio, tooth body width, airgap and magnet thickness of magnet in PM motor with asymmetry stator design are carried out and the performance verification are referred to the back-emf, average output torque, torque ripple as well as cogging torque. From the investigation using 2D-Finite Element Analysis, optimum size of tooth body width and optimum number of coil turns result better output torque while other sizing approaches result no significant change as quick saturation took place.
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JUNG, JI-YONG, und JUNG-JA KIM. „INFLUENCE OF CUSTOMIZED FOOT ORTHOTICS ON GAIT BALANCE FOR PELVIC ASYMMETRY PATIENTS“. Journal of Mechanics in Medicine and Biology 19, Nr. 05 (August 2019): 1950039. http://dx.doi.org/10.1142/s0219519419500398.
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Gait is one of the most common and important factor of human movements in daily life. Pelvis is closely connected with the gait due to it allows maintain stable posture by supporting the spine and lower extremities against the gravity. Therefore, pelvic asymmetry, which is caused by biomechanical stress and muscle imbalance, has been associated with postural imbalance and abnormal walking pattern. The purpose of this study was to manufacture customized foot orthotics for improving gait balance and evaluate the effectiveness of customized foot orthotics during walking by measuring lower extremity muscle activity and plantar pressure distribution. All subjects with pelvic asymmetry were asked to walk on a treadmill under three conditions: walking without foot orthotics, walking with customized foot orthotics and walking with non-customized foot orthotics. Root mean square (RMS) value of the electromyography signals, force and peak pressure of the plantar pressure distribution was analyzed based on the gait cycle. The results showed that excessive tension of the muscles and high pressure of the foot that was induced by pelvic asymmetry were more reduced when walking with custom-made foot orthotics than walking without foot orthotics and walking with non-customized foot orthotics. This paper suggest that custom-made orthotics for patients with pelvic asymmetry could be helpful to relieve the excessive loading of the foot and maintain balanced gait pattern.
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Dahoua, Lamri, und Fakhridine Boymatov. „Endurance of the wooden bridge reinforced by the dowel plates“. Studia Geotechnica et Mechanica 40, Nr. 3 (20.10.2018): 202–7. http://dx.doi.org/10.2478/sgem-2018-0023.
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Abstract The most important piece of road infrastructure is bridges. Wooden bridges have advanced constantly during the past decades. The trend began in Scandinavian countries but has also now gained significant ground in Russia. This research studies experimental endurance potential of the joints of the wooden beam while considering the coefficient of asymmetry of the cycle, which corresponds to the actual operating conditions. Performance analysis of the composite bars is carried out based on the experiment; the development of a special methodology for calculating the joints of wooden elements with the dowel plates for their better endurance is also introduced in this paper. The results of experimental studies on the performance of bending composite wooden bridge bars based on dowel plates operating under cyclic influences thus determine the endurance limit of wood for composite wooden bridge beams based on dowel plates. The calculation technique and interdependence of the endurance coefficient affecting the asymmetry coefficient of the bent composite wooden bridge bars on the dowel plates under cyclic loading are considered. The experimental data on the endurance of composite wooden bridge beams have been obtained, and separate analysis has been made of the compounds under cyclic loading performance; a method has been developed for calculating the bent composite wooden bridge bars reinforced by the dowel plates under cyclic influences.
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Troshchenko, V. T., V. V. Pokrovskii, V. G. Kaplunenko und B. T. Timofeev. „Effect of the dimensions of specimens and of cycle asymmetry on the regularities of unstable crack propagation under cyclic loading“. Strength of Materials 19, Nr. 3 (März 1987): 287–93. http://dx.doi.org/10.1007/bf01524121.
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21
Lu, Damin, Shuai Wang, Yongting Lan, Keshi Zhang, Wujun Li und Qixi Li. „Statistical Analysis of Grain-Scale Effects of Twinning Deformation for Magnesium Alloys under Cyclic Strain Loading“. Materials 13, Nr. 11 (28.05.2020): 2454. http://dx.doi.org/10.3390/ma13112454.
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To reveal the relationship between grain size and twinning deformation of magnesium alloys under cyclic strain, this study carried out a group of strain-controlled low-cycle fatigue experiments and statistical analysis of microstructures. Experimental results show that the shape of the hysteresis loop exhibits significant asymmetry at different strain amplitudes, and the accumulation of residual twins plays an important role in subsequent cyclic deformation. For the different strain amplitudes, the statistical distribution of the grain size of magnesium alloy approximately follows the Weibull probability function distribution, while the statistical distribution of twin thickness is closer to that of Gaussian probability function. The twin nucleation number (TNN) increases with the increase of grain size, but there is no obvious function relationship between twin thickness and grain size. Twin volume fraction (TVF) increases with the increase of grain size, which is mainly due to the increase of TNN. This work can provide experimental evidence for a more accurate description of the twinning deformation mechanism.
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Roşca, Valcu, und Cosmin Mihai Miriţoiu. „The Crack Length Growth – A Fracture Parameter in a Stainless Steel Influenced by the Loading Test“. Applied Mechanics and Materials 823 (Januar 2016): 489–94. http://dx.doi.org/10.4028/www.scientific.net/amm.823.489.
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The defects or micro-cracks that exist in a product mass from the elaboration phase, can extend controlled or not, because of a variable solicitation applied to a product or a sample. The Fracture Mechanics parameter that highlight the crack propagation in time is its rate growth marked as da/dN and represents the crack advancement length during a solicitation cycle. This can be studied based on some mathematical models obtained from some propose models, experimentally determined. In this paper, a propagation process analysis is made of a fracture crack by an axial-eccentric fatigue loading for a 10TiNiCr175 stainless steel. CT type flat samples were loaded with an asymmetry coefficient R= 0.3, for the solicitation temperatures: T= 293K (20°C), T= 253K (-20°C), respectively T= 213 K (-60°C). The crack growth increase was studied by three most used mathematical models: the polynomial method standardized according to ASTM E647, method proposed by Paris and method proposed by Walker.
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Andrews, E., P. J. Sheridan und J. A. Ogren. „Seasonal differences in the vertical profiles of aerosol optical properties over rural Oklahoma“. Atmospheric Chemistry and Physics Discussions 11, Nr. 4 (18.04.2011): 11939–57. http://dx.doi.org/10.5194/acpd-11-11939-2011.
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Abstract. A small airplane made more than 450 aerosol optical property (light absorption and light scattering) vertical profile measurements (up to 4 km) over a rural Oklahoma site between March 2000 and July 2005. These profiles suggest significant seasonal differences in aerosol properties. The highest amounts of scattering and absorbing aerosol are observed during the summer, while the relative contribution of aerosol absorption is highest in the winter (i.e., single scattering albedo is lowest in winter). Aerosol absorption generally decreased with altitude below ∼1.5 km and then was relatively constant above that. Aerosol scattering decreased sharply with altitude below ∼1.5 km but, unlike absorption, also decreased at higher altitudes, albeit less sharply. The seasonal variability observed for aerosol loading is consistent with other aerosol measurements in the region including AERONET aerosol optical depth (AOD), CALIPSO vertical profiles, and IMPROVE aerosol mass. The column averaged single scattering albedo derived from in situ airplane measurements shows a similar seasonal cycle as the AERONET single scattering albedo inversion product, but a comparison of aerosol asymmetry parameter from airplane and AERONET platforms suggests differences in seasonal variability. The observed seasonal cycle of aerosol loading corresponds with changes in air mass back trajectories: the aerosol scattering was higher when transport was from polluted areas (e.g., the Gulf Coast) and lower when the air came from cleaner regions and/or the upper atmosphere.
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Winiarski, Slawomir, Alicja Rutkowska-Kucharska, Andrzej Pozowski und Krzysztof Aleksandrowicz. „A New Method of Evaluating the Symmetry of Movement Used to Assess the Gait of Patients after Unilateral Total Hip Replacement“. Applied Bionics and Biomechanics 2019 (01.12.2019): 1–11. http://dx.doi.org/10.1155/2019/7863674.
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Purpose. We propose a new concept of symmetry, the symmetry function, as a continuous function of the percentage of differences between sides of body movement and normalised throughout the whole range of motion. The method is used to assess the dynamical symmetry of gait of patients after unilateral total hip replacement (asymmetric group) and healthy people (symmetric group) and also to reveal discrepancies between normal and abnormal movement patterns. Methods. The gait of twelve male patients (49.7±2.8 y), six weeks after unilateral total hip replacement (uTHR), was analysed against the gait of thirteen healthy men (36.1±3.1 y). The speed of healthy men was matched to the speed of the patients. Comparison of the affected limb in uTHR patients with the healthy limb of able-bodied men was carried out on the basis of the highest symmetry values in the sagittal plane. Results. In uTHR patients, the symmetry function provides information on the symmetry of movements in the whole range of motion in contrast to symmetry indices which are calculated for selected parameters or peak values. Research revealed average asymmetric discrepancies for pelvic tilt up to 250% for the entire gait cycle with a peak of approx. 400% at the end of the loading response and terminal swing phases. Asymmetry of gait observed in other joints was below 200% of the mean range of motion. Conclusions. Regions of the greatest asymmetry in pathological movements are usually different from the region of the greatest range of motion. Therefore, it is insufficient to measure symmetry only for selected regions during motion. The symmetry function is a simple method which can complement other robust methods in time series data evaluation and interpretation.
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Springer, Shmuel, Uri Gottlieb und Mariya Lozin. „Spatiotemporal Gait Parameters as Predictors of Lower-Limb Overuse Injuries in Military Training“. Scientific World Journal 2016 (2016): 1–5. http://dx.doi.org/10.1155/2016/5939164.
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The study objective was to determine whether spatiotemporal gait parameters could predict lower-limb overuse injuries in cohort of combat soldiers during first year of military service. Newly recruited infantry soldiers walked on a treadmill at a 15° incline with a fixed speed of 1.67 m/sec while wearing a standard military vest with a 10 kg load. Stride time variability, stride length variability, step length asymmetry, and the duration of the loading response phase of the gait cycle were measured. Injury data on 76 soldiers who did not report musculoskeletal complaints at initial screening were collected one year after recruitment. Multiple logistic regression analyses were conducted to determine the predictive effect of the gait parameters on lower-limb injuries. Twenty-four soldiers (31.6%) had overuse injuries during the first year after recruitment. Duration of the loading response was a significant predictor of general lower-limb injury (p<0.05), as well as of foot/ankle and knee injuries (p<0.05,p<0.01, resp.). A cutoff value of less than 12.15% for loading response duration predicted knee injuries with 83% sensitivity and 67% specificity. This study demonstrates the utility of spatiotemporal gait evaluation, a simple screening tool before military training, which may help to identify individuals at risk of lower-limb overuse injuries.
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Belan, Juraj, Lenka Kuchariková, Alan Vaško, Eva Tillová, Mária Chalupová und Miloš Matvija. „The SEM and TEM Analysis of IN718 Alloy after Fatigue Push-Pull Loading at 700°C“. Defect and Diffusion Forum 405 (November 2020): 288–93. http://dx.doi.org/10.4028/www.scientific.net/ddf.405.288.
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Specimens from Ni-Cr-Fe wrought superalloy INCONEL 718 were used for fatigue push-pull test at elevated temperature 700 °C. Fatigue loading was with the coefficient of cycle asymmetry R = -1. Temperature of fatigue test was chosen from two reasons; one is that limit operating temperature for this type of alloy is 650 – 700 °C due to precipitation of stable but incoherent orthorhombic Ni3Nb delta phase; the second reason for this temperature is fact that metastable body-centred tetragonal Ni3Nb gamma double prime phase starts to transform to delta phase and from that reason there is an expectation for mechanical properties decreasing due to increased volume of delta phase. For evaluation of fatigued specimens were Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observation used. Also methods of quantitative metallography – coherent testing grids were used for evaluation of delta phase volume. Some references describe that higher volume of delta phase, mostly situated at grain boundaries, act as initiation sites for cracks and therefore decreasing mechanical properties. Employed SEM and TEM analysis confirm the increased volume of delta phase in specimens after fatigue loading but a negative influence on dynamic properties, such fatigue lifetime, for this alloy was not confirmed.
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Bondarev, B. A., A. O. Korneeva, O. O. Korneev, A. G. Saakyan und I. A. Vostrikov. „ENDURANCE OF CARCASS TYPE POLYMER COMPOSITE MATERIALS AT DEFORMATION JOINTS OF BRIDGE STRUCTURE’S ELEMENTS“. Construction and Geotechnics 11, Nr. 3 (15.12.2020): 29–40. http://dx.doi.org/10.15593/2224-9826/2020.3.03.
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Numerous studies of road surfaces in the areas of deformation joints of bridges and overpasses have shown that the use of polymer composite materials can significantly reduce cracks and destruction. The cyclic durability of such materials prevents rutting in the zone of deformation seams, due to their damping properties. Effective building materials based on furfural acetone monomers (FAM) are used for the manufacture of tides that experience cyclic impacts of vehicle wheels. Therefore, tests were conducted on the endurance of FAM polymer concrete under the influence of cyclic application of load. Today cyclic and static durability of traditional FAM polymer concretes has been studied in detail. However, the carcass technology can improve the characteristics of polymer concrete, in particular, reduce shrinkage. These polymer concretes are produced in two stages. First, a carcass is created from the filler grains glued together, and then the voids are filled with a matrix composition. This article presents the results of endurance tests of polymer concrete made using carcass and traditional technologies, with the same set of raw materials. To determine the limit of endurance, we used the method of planning an experiment with the construction of an orthogonal-composite plan of the second order. The cycle asymmetry coefficient and loading level (as a percentage of the destruction load) were selected as variable factors affecting the cyclic durability. Lines of fatigue strength of traditional polymer concrete FAM and obtained by carcass manufacturing technology at different values of the cycle asymmetry coefficient are also constructed. The results of endurance tests under the influence of repeated application of load showed that the polymer composite material based on furfural acetone monomer, obtained by carcass technology, has an increased cyclic durability compared to traditional polymer concrete.
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Tay, Hui W., Karin R. Bryan, Conrad A. Pilditch, Stephen Park und David P. Hamilton. „Variations in nutrient concentrations at different time scales in two shallow tidally dominated estuaries“. Marine and Freshwater Research 63, Nr. 2 (2012): 95. http://dx.doi.org/10.1071/mf11102.
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Water-quality observations in estuaries can be highly variable in time and space, making it difficult to quantify nutrient fluxes and to discriminate patterns. We measured nitrate, phosphate and ammonium concentrations in two shallow tidally dominated estuaries in Tauranga Harbour, New Zealand, during four periods (winter, start of spring, end of spring and summer) within 1 year, to determine the source of variability observed in a 19-year monitoring program. These measurements consisted of high-frequency monitoring during one 24-h period (covering a daytime flood-ebb tide and a night-time flood-ebb tide) at each estuary. Concentrations of nitrate and ammonium had distinctive tidal patterns, with rising values during ebb flows. This tidal asymmetry caused a net seaward flux of dissolved inorganic nitrogen (nitrate and ammonium), with higher exports at night. Net fluxes were 34–358 kg N per tidal cycle for nitrate and 22–93 kg N per tidal cycle for ammonium. Fluxes were large relative to previously published model-based predictions for the region, particularly during winter. Our results showed that estuarine sampling strategies need to account for tidal variability and the role of episodic runoff events, and highlighted the importance of correctly validated mass fluxes from field measurements for comparisons with nutrient-loading models.
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Böhm, Michał, Krzysztof Kluger, Sławomir Pochwała und Mariusz Kupina. „Application of the S-N Curve Mean Stress Correction Model in Terms of Fatigue Life Estimation for Random Torsional Loading for Selected Aluminum Alloys“. Materials 13, Nr. 13 (04.07.2020): 2985. http://dx.doi.org/10.3390/ma13132985.
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The paper presents the experimental fatigue test results for cyclic constant amplitude loading conditions for the case of the torsion of the PA4 (AW-6082-T6), PA6 (AW-2017A-T4) and PA7 (AW-2024-T3) aluminum alloy for a drilled diabolo type test specimen. The tests have been performed for the stress asymmetry ratios R = −1, R = −0.7, R = −0.5 and R = −0.3. The experimental results have been used in the process of a fatigue life estimation performed for a random generated narrowband stress signal with a zero and a non-zero global mean stress value. The calculations have been performed within the time domain with the use of the rainflow cycle counting method and the Palmgren−Miner damage hypothesis. The mean stress compensation has been performed with the S-N curve mean stress model proposed by Niesłony and Böhm. The model has been modified in terms of torsional loading conditions. In order to obtain an appropriate R = 0 ratio S-N curve fatigue strength amplitude, the Smith−Watson−Topper model was used and compared with literature fatigue strength amplitudes. The presented solution extends the use of the correction model in terms of the torsional loading condition in order to obtain new S-N curves for other R values on the basis of the R = −1 results. The work includes the computational results for new fatigue curves with and without the mean stress effect correction. The results of the computations show that the mean stress effect plays a major role in the fatigue life assessment of the tested aluminum alloys and that the method can be used to assess the fatigue life under random conditions.
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Vasechkin, M. A., S. V. Egorov, A. B. Kolomensky und E. D. Chertov. „Low-cycle fatigue of welded structures made from domestic and imported materials“. Proceedings of the Voronezh State University of Engineering Technologies 80, Nr. 4 (21.03.2019): 75–79. http://dx.doi.org/10.20914/2310-1202-2018-4-75-79.
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In various branches of modern engineering, corrosion-resistant steels and titanium alloys are widely used as structural materials. At the same time, it is possible to connect parts made from domestic and imported alloys using automatic argon-arc electric welding, which leads to the formation of a material with unexplored properties in the weld. Welded joints are stress concentrators and currently there is no information about low-cycle fatigue of welded joints obtained by fusing domestic and imported materials. In the course of the research, the modes of welding and heat treatment of butt welded joints obtained from sheet titanium alloys and corrosion-resistant steel of domestic and foreign production have been developed. Resource tests for low-cycle fatigue of samples of welded joints were carried out. Tests on low-cycle fatigue were carried out on the upgraded testing machine UMM-10 with repeated static stretching with an asymmetry factor of +0.1 and at a frequency of 0.6–0.8 Hz. The maximum tensile stress was 80% of the temporary tensile strength of the weakest alloy in the pair. The main stress axis from external loading in all cases was perpendicular to the weld. The tests were carried out until the destruction of the sample. As a result of research, it was established that all welded joints were destroyed along the fusion line, which is explained by the simultaneous action of geometric and structural stress concentrators. In this case, the destruction of the samples, as a rule, began near the seam from the side of the weakest alloy in the pair. It was also established that the use of temperatures of incomplete annealing in comparison with the full one allows to increase the cyclic durability for welded joints of titanium alloys by 1.3–2 times. From the results of comparative tests of samples of corrosion-resistant steels, it follows that domestic and imported steels, as well as their welded joints, have similar properties, both in strength and in re-static durability.
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Andrews, E., P. J. Sheridan und J. A. Ogren. „Seasonal differences in the vertical profiles of aerosol optical properties over rural Oklahoma“. Atmospheric Chemistry and Physics 11, Nr. 20 (27.10.2011): 10661–76. http://dx.doi.org/10.5194/acp-11-10661-2011.
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Abstract. A small airplane made 597 aerosol optical property (light absorption and light scattering) vertical profile measurements over a rural Oklahoma site between March 2000 and December 2007. The aerosol profiles obtained during these 8 yr of measurements suggest significant seasonal differences in aerosol loading (scattering and absorption). The highest amounts of scattering and absorbing aerosol are observed during the summer and the lowest loading occurs during the winter. The relative contribution of aerosol absorption is highest in the winter (i.e., single scattering albedo is lowest in winter), particularly aloft. Aerosol absorption generally decreased with altitude below ~1.5 km and then was relatively constant or decreased more gradually above that. Aerosol scattering decreased sharply with altitude below ~1.5 km but, unlike absorption, also decreased at higher altitudes, albeit less sharply. Scattering Ångström exponents suggest that the aerosol was dominated by sub-micron aerosol during the summer at all altitudes, but that larger particles were present, especially in the spring and winter above 1 km. The seasonal variability observed for aerosol loading is consistent with AERONET aerosol optical depth (AOD) although the AOD values calculated from in situ adjusted to ambient conditions and matching wavelengths are up to a factor of two lower than AERONET AOD values depending on season. The column averaged single scattering albedo derived from in situ airplane measurements are similar in value to the AERONET single scattering albedo inversion product but the seasonal patterns are different – possibly a consequence of the strict constraints on obtaining single scattering albedo from AERONET data. A comparison of extinction Ångström exponent and asymmetry parameter from the airplane and AERONET platforms suggests similar seasonal variability with smaller particles observed in the summer and fall and larger particles observed in spring and winter. The observed seasonal cycle of aerosol loading corresponds with changes in air mass back trajectories: the aerosol scattering was higher when transport was from polluted areas (e.g., the Gulf Coast) and lower when the air came from cleaner regions and/or the upper atmosphere.
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Černý, Ivo, und Dagmar Mikulová. „Evaluation of Overloading and Crack Closure Effects on Fatigue Crack Growth in an Aircraft 7075-T7351 Al-Alloy“. Key Engineering Materials 577-578 (September 2013): 325–28. http://dx.doi.org/10.4028/www.scientific.net/kem.577-578.325.
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Al 7075 alloy is a high strength material usually used for highly stressed components in lightweight structures, typically in aircraft, aerospace and defence applications. It can be applied in different heat treatment conditions, but the T7351 temper state is most widely used because of improved stress-corrosion cracking resistance. An investigation of effects of overloads on fatigue crack growth (FCG) and retardation in Al 7075-T7351 alloy was carried out. FCG rates were measured at load asymmetry R = Fmin / Fmax = 0.1, in quite wide region of growth between 10-8 and 10-5 m/cycle (stress intensity factor range ΔK between 6 and 40 MPa m1/2). Retardation effects of overloads of the magnitudes 2.7-times and 3.0-times of the maximum load in the constant range fatigue loading were significant. Crack mouth opening displacement was evaluated at numerous stages of crack growth including pre-cracking with so called load shedding method. The overloads resulted in substantial crack closure effects, which, however, did not occur immediately after the overloading, but after further fatigue crack extension. Results are discussed considering both theoretically and experimentally estimated plastic zone size and considering crack closure issues recently published in the literature
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Tatarelli, Antonella, Mariano Serrao, Tiwana Varrecchia, Lorenzo Fiori, Francesco Draicchio, Alessio Silvetti, Silvia Conforto, Cristiano De Marchis und Alberto Ranavolo. „Global Muscle Coactivation of the Sound Limb in Gait of People with Transfemoral and Transtibial Amputation“. Sensors 20, Nr. 9 (29.04.2020): 2543. http://dx.doi.org/10.3390/s20092543.
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The aim of this study was to analyze the effect of the level of amputation and various prosthetic devices on the muscle activation of the sound limb in people with unilateral transfemoral and transtibial amputation. We calculated the global coactivation of 12 muscles using the time-varying multimuscle coactivation function method in 37 subjects with unilateral transfemoral amputation (10, 16, and 11 with mechanical, electronic, and bionic prostheses, respectively), 11 subjects with transtibial amputation, and 22 healthy subjects representing the control group. The results highlighted that people with amputation had a global coactivation temporal profile similar to that of healthy subjects. However, amputation increased the level of the simultaneous activation of many muscles during the loading response and push-off phases of the gait cycle and decreased it in the midstance and swing subphases. This increased coactivation probably plays a role in prosthetic gait asymmetry and energy consumption. Furthermore, people with amputation and wearing electronic prosthesis showed lower global coactivation when compared with people wearing mechanical and bionic prostheses. These findings suggest that the global lower limb coactivation behavior can be a useful tool to analyze the motor control strategies adopted and the ability to adapt to the prosthetic device.
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Pandolfi, M., A. Ripoll, X. Querol und A. Alastuey. „Climatology of aerosol optical properties and black carbon mass absorption cross section at a remote high altitude site in the Western Mediterranean Basin“. Atmospheric Chemistry and Physics Discussions 14, Nr. 3 (11.02.2014): 3777–814. http://dx.doi.org/10.5194/acpd-14-3777-2014.
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Abstract. Aerosol light scattering, backscattering and absorption were measured at Montsec (MSC; 42°3' N, 0°44' E, 1570 m a.s.l.), a remote high-altitude site in the Western Mediterranean Basin. Mean (± sd) scattering, hemispheric backscattering and absorption were 18.9 ± 20.8 Mm−1, 2.6 ± 2.8 Mm−1 and 1.5 ± 1.4 Mm−1, respectively at 635 nm during the period under study (June 2011–June 2013). Mean values of single scattering albedo (635 nm), scattering Ångström exponent (450–635 nm), backscatter-to-scatter ratio (635 nm), asymmetry parameter (635 nm) and black carbon mass absorption cross section (637 nm) were 0.92 ± 0.03, 1.56 ± 0.88, 0.16 ± 0.09, 0.53 ± 0.16 and 10.9 ± 3.5 m2 g−1 respectively. The scattering measurements performed at MSC locate this site in the medium/upper range of values reported for other mountaintop sites in Europe mainly due to the frequent African dust episodes and regional recirculation scenarios occurring mostly in spring/summer and causing the presence of polluted layers at the MSC altitude. Under these conditions no clear diurnal cycles were observed for the measured extensive aerosol optical properties (scattering, absorption and extinction). Conversely, the mean particle absorption at MSC was relatively lower compared with other EU remote stations thus leading to relatively higher single scattering albedo compared with most European data. A season-dependent decrease in the magnitude of aerosol extensive properties was observed when MSC was in the free troposphere with the highest free-troposphere vs. all-data difference observed in winter and the lowest in spring/summer. The slope of the scattering vs. absorption relationship (among the lowest reported for other mountain top sites worldwide) indicates that the MSC site is dominated by dust aerosols at high aerosol loading. Correspondingly, scattering Ångström exponent and asymmetry parameter respectively decreased and increased indicating the shift toward larger particles associated with African dust episodes. The black carbon mass absorption cross section showed a clear annual cycle with higher values in summer when the occurrence of African dust outbreaks and regional recirculation scenarios favour the presence of aged black carbon particles in polluted layers at the MSC altitudes. The optical measurements performed at the MSC remote site were compared with those simultaneously performed at a regional background station in the Western Mediterranean Basin.
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Barrera, Javier Alejandro, Rafael Pedro Fernandez, Fernando Iglesias-Suarez, Carlos Alberto Cuevas, Jean-Francois Lamarque und Alfonso Saiz-Lopez. „Seasonal impact of biogenic very short-lived bromocarbons on lowermost stratospheric ozone between 60° N and 60° S during the 21st century“. Atmospheric Chemistry and Physics 20, Nr. 13 (13.07.2020): 8083–102. http://dx.doi.org/10.5194/acp-20-8083-2020.
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Abstract. Biogenic very short-lived bromocarbons (VSLBr) currently represent ∼25 % of the total stratospheric bromine loading. Owing to their much shorter lifetime compared to anthropogenic long-lived bromine (e.g. halons) and chlorine (e.g. chlorofluorocarbons), the impact of VSLBr on ozone peaks in the lowermost stratosphere, which is a key climatic and radiative atmospheric region. Here we present a modelling study of the evolution of stratospheric ozone and its chemical loss within the tropics and at mid-latitudes during the 21st century. Two different experiments are explored: considering and neglecting the additional stratospheric injection of 5 ppt biogenic bromine naturally released from the ocean. Our analysis shows that the inclusion of VSLBr results in a realistic stratospheric bromine loading and improves the agreement between the model and satellite observations of the total ozone column (TOC) for the 1980–2015 period at mid-latitudes. We show that the overall ozone response to VSLBr at mid-latitudes follows the stratospheric evolution of long-lived inorganic chlorine and bromine throughout the 21st century. Additional ozone loss due to VSLBr is maximized during the present-day period (1990–2010), with TOC differences of −8 DU (−3 %) and −5.5 DU (−2 %) for the Southern Hemisphere and Northern Hemisphere mid-latitudes (SH-MLs and NH-MLs), respectively. Moreover, the projected TOC differences at the end of the 21st century are ∼50 % lower than the values found for the present-day period. We find that seasonal VSLBr impact on lowermost stratospheric ozone at mid-latitude is influenced by the seasonality of the heterogeneous inorganic-chlorine reactivation processes on ice crystals. Indeed, due to the more efficient reactivation of chlorine reservoirs (mainly ClONO2 and HCl) within the colder SH-ML lowermost stratosphere, the seasonal VSLBr impact shows a small but persistent hemispheric asymmetry through the whole modelled period. Our results indicate that, although the overall VSLBr-driven ozone destruction is greatest during spring, the halogen-mediated (Halogx-Loss) ozone loss cycle in the mid-latitude lowermost stratosphere during winter is comparatively more efficient than the HOx cycle with respect to other seasons. Indeed, when VSLBr are considered, Halogx-Loss dominates wintertime lowermost stratospheric ozone loss at SH-MLs between 1985 and 2020, with a contribution of inter-halogen ClOx–BrOx cycles to Halogx-Loss of ∼50 %. Within the tropics, a small (<-2.5 DU) and relatively constant (∼-1 %) ozone depletion mediated by VSLBr is closely related to their fixed emissions throughout the modelled period. By including the VSLBr sources, the seasonal Halogx-Loss contribution to lowermost stratospheric ozone loss is practically dominated by the BrOx cycle, reflecting the low sensitivity of very short-lived (VSL) bromine to background halogen abundances to drive tropical stratospheric ozone depletion. We conclude that the link between biogenic bromine sources and seasonal changes in heterogeneous chlorine reactivation is a key feature for future projections of mid-latitude lowermost stratospheric ozone during the 21st century.
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Gulgazli, Alasgar, und Ali Hikmat Ahmadov. „CYCLIC TORSION WITH INTERNAL PRESSURE OF PRE-STRETCHED THIN-WALLED CYLINDERS“. ETM - Equipment, Technologies, Materials 05, Nr. 01 (20.01.2021): 21–24. http://dx.doi.org/10.36962/swd0202202021.
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The article considers the following two tasks. 1) Strength calculations are carried out for a long thin-walled cylinder, the ends of which are not closed during reloading. At the first loading, the thin-walled cylinder is stretched by a longitudinal force leading to longitudinal plastic deformations. When reloaded, the cylinder twists and at the same time uniform pressure acts from the inside. It is noted that, in particular, the shaft of wind generators is subjected to such loading. It is proved that the equation of the yield curve in the plane of the normal and tangential stresses of the stress space is an ellipse, whose semi axes are a function of the mechanical characteristics of the material and the residual stresses after the first loading. 2) We consider cyclic twisting with internal pressure of pre-stretched thin-walled cylinders. The yield surface equation is obtained for a thin-walled cylinder under repeated loading τ + p. which stretched upon first loading. It is proved that the yield surface equations also yield the fatigue surface equations if the yield stress σ_(T.) is replaced by the fatigue stress σ_(0.) Expressions are found for the number of cycles required for fatigue failure under an asymmetric loading cycle under repeated loading. It is proved that in order to increase the number of cycles required for fatigue fracture, during the first loading, when the material is strengthened due to plastic deformation, and with repeated cyclic loading, the same stress components must take place. It is proved that if during repeated loading the end of the loading path is inside the endurance surface, then the number of cycles required for fatigue failure in an asymmetric loading cycle tends to infinity. Keywords: Initial loading, reloading, cyclic loading, strength, fatigue failure, plastic deformation, residual stress, yield surface.
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Sherman, James P., und Allison McComiskey. „Measurement-based climatology of aerosol direct radiative effect, its sensitivities, and uncertainties from a background southeast US site“. Atmospheric Chemistry and Physics 18, Nr. 6 (26.03.2018): 4131–52. http://dx.doi.org/10.5194/acp-18-4131-2018.
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Abstract. Aerosol optical properties measured at Appalachian State University's co-located NASA AERONET and NOAA ESRL aerosol network monitoring sites over a nearly four-year period (June 2012–Feb 2016) are used, along with satellite-based surface reflectance measurements, to study the seasonal variability of diurnally averaged clear sky aerosol direct radiative effect (DRE) and radiative efficiency (RE) at the top-of-atmosphere (TOA) and at the surface. Aerosol chemistry and loading at the Appalachian State site are likely representative of the background southeast US (SE US), home to high summertime aerosol loading and one of only a few regions not to have warmed during the 20th century. This study is the first multi-year ground truth DRE study in the SE US, using aerosol network data products that are often used to validate satellite-based aerosol retrievals. The study is also the first in the SE US to quantify DRE uncertainties and sensitivities to aerosol optical properties and surface reflectance, including their seasonal dependence.Median DRE for the study period is −2.9 W m−2 at the TOA and −6.1 W m−2 at the surface. Monthly median and monthly mean DRE at the TOA (surface) are −1 to −2 W m−2 (−2 to −3 W m−2) during winter months and −5 to −6 W m−2 (−10 W m−2) during summer months. The DRE cycles follow the annual cycle of aerosol optical depth (AOD), which is 9 to 10 times larger in summer than in winter. Aerosol RE is anti-correlated with DRE, with winter values 1.5 to 2 times more negative than summer values. Due to the large seasonal dependence of aerosol DRE and RE, we quantify the sensitivity of DRE to aerosol optical properties and surface reflectance, using a calendar day representative of each season (21 December for winter; 21 March for spring, 21 June for summer, and 21 September for fall). We use these sensitivities along with measurement uncertainties of aerosol optical properties and surface reflectance to calculate DRE uncertainties. We also estimate uncertainty in calculated diurnally-averaged DRE due to diurnal aerosol variability. Aerosol DRE at both the TOA and surface is most sensitive to changes in AOD, followed by single-scattering albedo (ω0). One exception is under the high summertime aerosol loading conditions (AOD ≥ 0.15 at 550 nm), when sensitivity of TOA DRE to ω0 is comparable to that of AOD. Aerosol DRE is less sensitive to changes in scattering asymmetry parameter (g) and surface reflectance (R). While DRE sensitivity to AOD varies by only ∼ 25 to 30 % with season, DRE sensitivity to ω0, g, and R largely follow the annual AOD cycle at APP, varying by factors of 8 to 15 with season. Since the measurement uncertainties of AOD, ω0, g, and R are comparable at Appalachian State, their relative contributions to DRE uncertainty are largely influenced by their (seasonally dependent) DRE sensitivity values, which suggests that the seasonal dependence of DRE uncertainty must be accounted for. Clear sky aerosol DRE uncertainty at the TOA (surface) due to measurement uncertainties ranges from 0.45 (0.75 W m−2) for December to 1.1 (1.6 W m−2) for June. Expressed as a fraction of DRE computed using monthly median aerosol optical properties and surface reflectance, the DRE uncertainties at TOA (surface) are 20 to 24 % (15 to 22 %) for March, June, and September and 49 (50 %) for DEC. The relatively low DRE uncertainties are largely due to the low uncertainty in AOD measured by AERONET. Use of satellite-based AOD measurements by MODIS in the DRE calculations increases DRE uncertainties by a factor of 2 to 5 and DRE uncertainties are dominated by AOD uncertainty for all seasons. Diurnal variability in AOD (and to a lesser extent g) contributes to uncertainties in DRE calculated using daily-averaged aerosol optical properties that are slightly larger (by ∼ 20 to 30 %) than DRE uncertainties due to measurement uncertainties during summer and fall, with comparable uncertainties during winter and spring.
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Ding, Zhi Ping, Jun Zeng, Xiao Peng Bai und Jian Hui Fang. „Simulation on Stress Relaxation of DD3 Nickel-Based Single Crystal Superalloy Based on Micro-Cell Model“. Advanced Materials Research 834-836 (Oktober 2013): 1557–62. http://dx.doi.org/10.4028/www.scientific.net/amr.834-836.1557.
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Tension-torsion experiments at 680°C and 850°C on thin-wall tube specimens of DD3 nickel-based single crystal superalloys were successfully completed. It shows that specimens have stress relaxation obviously and inelastic deformation accumulation phenomenon with different crystal orientation under asymmetric cyclic loadings. Based on the microstructure characteristics of nickel-based single crystal superalloys, a two-phase multi-cell microscopic mechanical model was established by finite element method to simulate the test with displacement. Numerical simulation studies showed that the matrix phase appeared plastic deformation accumulation at first and resulted in low cycle fatigue damage, but stress distortion occurred on the boundary with a single cell model under tension-torsion displacement loading, which is not consistent with experimental results. While using multi-cell model can avoid this phenomenon, it could be better to simulate stress relaxation behavior under asymmetric cyclic loading at elevated temperature and to study on stress weaken damage for single crystal superalloys.
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Zhang, Junhong, Weidong Li, Huwei Dai, Nuohao Liu und Jiewei Lin. „Study on the Elastic–Plastic Correlation of Low-Cycle Fatigue for Variable Asymmetric Loadings“. Materials 13, Nr. 11 (28.05.2020): 2451. http://dx.doi.org/10.3390/ma13112451.
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The mean stress effect in fatigue life varies by material and loading conditions. Therefore, a classical low cycle fatigue (LCF) model based on mean stress correction shows limits in asymmetric loading cases in both accuracy and applicability. In this paper, the effect of strain ratio (R) on LCF life is analyzed and a strain ratio-based model is presented for asymmetric loading cases. Two correction factors are introduced to express correlations between strain ratio and fatigue strength coefficient and between strain ratio and fatigue ductility coefficient. Verifications are conducted through four materials under different strain ratios: high-pressure tubing steel (HPTS), 2124-T851 aluminum alloy, epoxy resin and AZ61A magnesium alloy. Compared with current widely used LCF models, the proposed model shows a better life prediction accuracy and higher potential in implementation in symmetric and asymmetric loading cases for different materials. It is also found that the strain ratio-based correction is able to consider the damage of ratcheting strain that the mean stress-based models cannot.
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Mehrabi, Hamed, Richard (Chunhui) Yang und Baolin Wang. „Effects of Tension–Compression Asymmetry on Bending of Steels“. Applied Sciences 10, Nr. 9 (11.05.2020): 3339. http://dx.doi.org/10.3390/app10093339.
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Stainless steels (SUS) and dual-phase (DP) steels have tension-compression asymmetry (TCA) in mechanical responses to full loading cycles. This phenomenon can significantly influence sheet metal forming of such metals, however, it is difficult to describe this behaviour analytically. In this research, a novel analytical method for asymmetric elastic-plastic pure bending using the Cazacu–Barlat 2004 asymmetric yield function is proposed. It only uses material parameters in tension along with an asymmetry coefficient related to the yield function. Bending operations of SUS304 and DP980 are investigated as two case studies. In the pure bending for both SUS304 and DP980, moment–curvature diagrams are analytically obtained. Furthermore, linear and nonlinear springback behaviours of SUS304 are analytically investigated. Moreover, using the analytical model as a user-defined material, a numerical model is developed for both steels under pure bending. In the V-bending case of SUS304 with and without TCA effects, the springback behaviours of the material are investigated numerically. In addition, considering friction effects, the analytical method is further modified for predicting springback behaviours in the V-bending of 16 types of SUS304 with various strengths are determined. All the analytical and numerical results have good agreement with those experimental results from literature for validation.
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Gorbovets, M. A., I. A. Khodinev, M. S. Belyaev und P. V. Ryzhkov. „Low-Cycle Fatigue of a VZh175 Nickel Superalloy during Asymmetric Loading“. Russian Metallurgy (Metally) 2019, Nr. 9 (September 2019): 889–93. http://dx.doi.org/10.1134/s0036029519090039.
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Zhang, Yixiang, Masahiko Miyauchi und Steven Nutt. „Effects of thermal cycling on phenylethynyl-terminated PMDA-type asymmetric polyimide composites“. High Performance Polymers 31, Nr. 7 (03.10.2018): 861–71. http://dx.doi.org/10.1177/0954008318804046.
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The effects of thermal cycling on a polymerized monomeric reactant (PMR) type polyimide (TriA X) reinforced with carbon fibers were investigated. Composite specimens were subjected to 2000 thermal cycles between −54°C and 232°C. At 400-cycle intervals, laminates were inspected for microcracks, and glass transition temperature ( T g) and short-beam shear (SBS) strength were measured. The composites did not exhibit microcracks after thermal cycling, although after 2000 thermal cycles, mechanical properties of the matrix declined slightly. The matrix degradation decreased the resistance to microcracking upon further loading. No effects of thermal oxidative aging were observed from thermal cycling, and thermally driven fatigue and creep were identified as the primary and secondary factors inducing mechanical degradation of the matrix. T g of the composites exhibited no change after 2000 cycles, while the SBS strength decreased slightly (3–9%). The results highlight the potential for use of TriA X composites as long-term structural components in high-temperature service environments.
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Borodii, M. V. „Modeling of the asymmetric low-cycle loading in the space of stresses“. Strength of Materials 30, Nr. 5 (September 1998): 472–80. http://dx.doi.org/10.1007/bf02522629.
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Fahimi, Pouya, Amin Hajarian, Amir Hossein Eskandari, Ali Taheri und Mostafa Baghani. „Asymmetric bending response of shape memory alloy beam with functionally graded porosity“. Journal of Intelligent Material Systems and Structures 31, Nr. 16 (20.07.2020): 1935–49. http://dx.doi.org/10.1177/1045389x20942323.
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In this study, an innovative semi-analytical model is presented to simulate the bending behavior of a shape memory alloy porous beam throughout loading and unloading cycles. The basis of the proposed method is the improved Brinson model which can capture the asymmetry behaviors of shape memory alloys in tension and compression. The comparison of the semi-analytical solution with two-dimensional finite element analysis results for both symmetric and asymmetric models of a homogeneous shape memory alloy beam is presented for model validation. Afterward, bending analysis of shape memory alloy beams with uniform porosity and functionally grading porosity is studied. For this purpose, first, the bending analysis of a shape memory alloy beam with uniform porosity is investigated to show the effects of porosity coefficient on the free tip deflection and slope. Then, the bending analysis of a shape memory alloy beam with functionally grading porosity is simulated. Reported findings with respect to symmetric and asymmetric models indicate that raising the porosity coefficient brings about an increase in deflection and slope. Also, it highlights the significant difference between the results of the asymmetric and symmetric models. The proposed semi-analytical solution can be utilized as an efficient tool for studying the effects of changing any of the porosity coefficient, the geometry, and material of shape memory alloy beams.
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Atig, Akram, Rabii Ben Sghaier, Raoudha Seddik und Raouf Fathallah. „Reliability-based high cycle fatigue design approach of parabolic leaf spring“. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 233, Nr. 4 (06.01.2017): 588–602. http://dx.doi.org/10.1177/1464420716680499.
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It is well established that the fatigue phenomenon of metallic structures such as leaf springs presents a random behavior, which is influenced by a probabilistic effect of many factors. This paper presents a probabilistic design approach to predict the high cycle fatigue behavior of a single asymmetric parabolic leaf spring. The suggested approach is used to assess the fatigue reliability of a single asymmetric parabolic leaf spring with uncertainties associated with its design parameters. This approach is based on the Gerber fatigue criterion, response surface method, and finite element model of the single asymmetric parabolic leaf spring. Two models of single asymmetric parabolic leaf spring are proposed: an analytical model based on the response surface method and a finite element one. To estimate the fatigue resistance according to the Gerber criterion, the probabilistic approach is developed using the “strength-load” method and the Monte Carlo simulation method. The dispersion of geometrical, applied loading, and material properties are taken into consideration. A comparison between fatigue reliability values, calculated by the application of Monte Carlo simulation method on the finite element and response surface models, indicates a good correlation between different method results.
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Klemenc, Jernej, Domen Seruga und Marko Nagode. „A Durability Prediction for the Magnesium Alloy AZ31 based on Plastic and Total Energy“. Metals 9, Nr. 9 (03.09.2019): 973. http://dx.doi.org/10.3390/met9090973.
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Magnesium has a good strength-to-weight ratio. As a result, magnesium alloys are gradually becoming an integral part of lightweight designs that are especially important to the automotive and aerospace industries. The magnesium alloy AZ31 is particularly suitable for forming. Furthermore, as its cyclic response is asymmetric, the accumulated energy during loading is a convenient basis for durability predictions of a product that is made of the AZ31 alloy. In this article, we show how the inverse-power law model can be combined with a Weibull’s probability density function to describe the shape of the fatigue-life curves and their scatter. Various load histories were chosen to characterize the response of the AZ31 alloy under different cyclic loadings. Both the plastic and the total strain energy densities were calculated for all the load histories, and then, a suitable dependence in terms of energy fatigue-life curves was determined. The proposed model is appropriate for modeling the low-cycle fatigue life of the AZ31 alloy. With the application of a linear damage-accumulation rule, it is also possible to predict the fatigue life for the non-constant amplitude loading within one decade of accuracy.
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Plashchynska, Alla. „To the modelling of the fatigue cracks propagation in a thin isotropic plates under biaxial asymmetric tension-compression“. Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, Nr. 1 (2019): 154–57. http://dx.doi.org/10.17721/1812-5409.2019/1.35.
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The modelling of the fatigue fracture process of the thin isotropic infinite plates with cracks under external biaxial asymmetric cyclic loading is considered. The solution of the problem is based on the joint consideration of the fracture mechanics and continuous damage mechanics concepts and using two types of equivalent stress criteria’s. The first one reduces an asymmetrical cyclic load to the equivalent symmetric cyclic load in time of the rupture. The second one reduces a plane stress state in the vicinity of the top crack to a single-axial one. The obtained system of equations of the model a relatively equivalent stress intensity factor allows us to determine the duration of the incubation stage and the rate of fatigue crack propagation in plates with different stress concentrators. The calculated dependences of the crack length, which extends from the circular hole, from the number of load cycles in the infinite aluminum plate with a circular hole at the variation of the parameters of the asymmetrical cycle and the coefficient of the biaxiality loading are constructed.
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Bennet-Clark, H. „Tymbal mechanics and the control of song frequency in the cicada Cyclochila australasiae“. Journal of Experimental Biology 200, Nr. 11 (01.01.1997): 1681–94. http://dx.doi.org/10.1242/jeb.200.11.1681.
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The anatomy of the tymbal of Cyclochila australasiae was re-described and the mass of the tymbal plate, ribs and resilin pad was measured. The four ribs of the tymbal buckle inwards in sequence from posterior to anterior. Sound pulses were produced by pulling the tymbal apodeme to cause the tymbal to buckle inwards. A train of four sound pulses, each corresponding to the inward buckling of one rib, could be produced by each inward pull of the apodeme, followed by a single pulse as the tymbal buckled outwards after the release of the apodeme. Each preparation produced a consistent sequence of pulses. Each of the pulses produced had its maximum amplitude during the first cycle of vibration. The waveform started with an initial inward-going rarefaction followed by a larger outward compression, followed by an approximately exponential decay, as is typical of a resonant system. The mean dominant frequencies of the pulses produced during the inward movement were 4.37, 4.19, 3.92 and 3.17 kHz respectively. The pulse produced during the outward movement had a mean resonant frequency of 6.54 kHz. This suggests that the mass-to-stiffness ratio that determines the resonant frequencies of the various pulses differs from pulse to pulse. If succeeding pulses followed rapidly, the next pulse tended to start on the inward-going half-cycle of its predecessor and to produce a coherent waveform. Coherence was lost if the preceding pulse had decayed to below approximately one-tenth of its peak amplitude. When the tymbal plate was loaded by a 380 µg wire weight, the resonant frequency of all sound pulses was reduced. Pulses produced later in the inward buckling sequence were less affected by the loading than earlier ones. This suggests that the effective mass determining the resonance in the later pulses is greater than that in the earlier pulses. The frequency of the pulses produced in the outward movement was affected most, suggesting that the mass involved was less than that in any of the pulses produced by the inward movement. The quality factor, Q, of the pulses produced by the inward buckling of the unloaded tymbal was approximately 10. For the outward buckling, Q was approximately 6. The Q of loaded tymbals was higher than than that of unloaded tymbals. The Q of the resonances varied approximately as the reciprocal of the resonant frequency. Experimental removal of parts of the tymbal showed that the thick dorsal resilin pad was an important elastic determinant of the resonant frequency, but that the mass and elasticity of the tymbal ribs were also determinants of the resonant frequency. The major element of mass is the tymbal plate. The integrity of the tymbal ribs was essential if the buckling movement were to occur. The force required to cause inward buckling of the tymbal was approximately 0.25 N. The force required to hold the tymbal in the buckled-in position was approximately 0.05 N. This asymmetry in the tymbal compliance, together with the different masses involved in inward and outward buckling, may account for the difference between the resonant frequencies of the inward-going and outward-going clicks. The tymbal appears to act as an energy storage mechanism that releases energy as the tymbal ribs buckle inwards in sequence. Each pulse provides a large initial impulse to the abdominal resonator, followed by a sustaining resonant vibration at, or close to, the song frequency. Subsequent pulses maintain the coherent resonance of the song pulse.
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Shekarian, A., und A. Varvani-Farahani. „Ratcheting behavior of notched stainless steel samples subjected to asymmetric loading cycles“. Journal of Iron and Steel Research International 28, Nr. 1 (19.08.2020): 86–97. http://dx.doi.org/10.1007/s42243-020-00465-2.
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Tang, Yongfu, Yanshuai Li, Wenfeng Guo, Jing Wang, Xiaomei Li, Shunji Chen, Shichun Mu, Yufeng Zhao und Faming Gao. „A highly ordered multi-layered hydrogenated TiO2-II phase nanowire array negative electrode for 2.4 V aqueous asymmetric supercapacitors with high energy density and long cycle life“. Journal of Materials Chemistry A 6, Nr. 2 (2018): 623–32. http://dx.doi.org/10.1039/c7ta09590b.
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A highly ordered binderfree multi-layered hydrogenated TiO2-II phase nanowire array (ML-HTO) negative electrode for 2.4 V aqueous asymmetric supercapacitors with high active materials loading, high electrical and ionic conductivity is synthesized via a multi-step method.