The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
F S Silva - One of the best experts on this subject based on the ideXlab platform.
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on a new temperature factor to predict the Fatigue Limit at different temperatures
International Journal of Fatigue, 2011Co-Authors: N Costa, F S SilvaAbstract:Abstract This study is concerned with a non-conventional Fatigue strength behavior of some materials with temperature. Notwithstanding the common reduction on Fatigue Limit of most materials with temperature, some materials show a non-conventional behavior, e.g. a temperature change from 20 °C to about 300 °C or 400 °C cause an increase in Fatigue Limit and/or tensile strength. The change in Fatigue Limit and tensile strength may have opposite trends. The existing ‘temperature effect’ parameters used in Fatigue Limit equations do not properly incorporate this non-conventional behavior. This study will propose a temperature factor that is able to properly incorporate the non-conventional behavior of some materials. It will also be shown that the new proposed temperature factor may be applied also to conventional materials with improved accuracy being than a more universal temperature factor.
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a new method for prediction of nodular cast iron Fatigue Limit
International Journal of Fatigue, 2010Co-Authors: Nuno Machado, Nuno Costa, F S SilvaAbstract:This paper is concerned with the ability of the different existing Fatigue strength theories to predict the Fatigue Limit of a nodular cast iron. Different studies exist on the effect of small defects, such as micro-shrinkage cavities or pores and graphite nodules (shape and size), and of microstructure, on the Fatigue strength of nodular cast iron. However poor Fatigue life predictions are obtained for the nodular cast iron with the existing models. It will be shown on this study that the role of geometrical features such as shape, size, and relative position of either casting defects as well as graphite nodules is an important parameter on the definition of the Fatigue Limit. A new correlation of Fatigue Limit with an improved accuracy as compared to existing models is proposed. The new model takes into consideration both intrinsic properties as well as some new geometrical material features.
Nuno Costa - One of the best experts on this subject based on the ideXlab platform.
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a new method for prediction of nodular cast iron Fatigue Limit
International Journal of Fatigue, 2010Co-Authors: Nuno Machado, Nuno Costa, F S SilvaAbstract:This paper is concerned with the ability of the different existing Fatigue strength theories to predict the Fatigue Limit of a nodular cast iron. Different studies exist on the effect of small defects, such as micro-shrinkage cavities or pores and graphite nodules (shape and size), and of microstructure, on the Fatigue strength of nodular cast iron. However poor Fatigue life predictions are obtained for the nodular cast iron with the existing models. It will be shown on this study that the role of geometrical features such as shape, size, and relative position of either casting defects as well as graphite nodules is an important parameter on the definition of the Fatigue Limit. A new correlation of Fatigue Limit with an improved accuracy as compared to existing models is proposed. The new model takes into consideration both intrinsic properties as well as some new geometrical material features.
N Ranganathan - One of the best experts on this subject based on the ideXlab platform.
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influence of casting defects on the Fatigue Limit of nodular cast iron
International Journal of Fatigue, 2004Co-Authors: Y Nadot, J Mendez, N RanganathanAbstract:The high cycle Fatigue behaviour of a nodular cast iron has been investigated under tension loading. Casting defects are at the origin of crack initiation for all samples tested. Critical defects (shrinkage) are located either at the surface or within the bulk. The role of the size and position of natural defect on the Fatigue Limit has been established. Results show that, for a given size, internal defects are less damaging than surface located ones. SEM observations revealed the existence of non-propagating surface cracks below the Fatigue Limit. By means of a marking technique, the 3D shape of these cracks initiated around the defects was fully described. In an attempt to simulate the evolution of the Fatigue Limit with defect size, some existing approaches are compared to experimental data; it is shown that 2D analysis of defects (crack or notch) is conservative.
Hiroshi Noguchi - One of the best experts on this subject based on the ideXlab platform.
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Fatigue Limit reliability of axisymmetric complex surface
International Journal of Fracture, 2020Co-Authors: Yuuta Aono, Hiroshi NoguchiAbstract:In this paper, a method to predict Fatigue Limit reliability of specimens with 2D complex rough surface is proposed. First, a effective surface profile on Fatigue Limit is proposed. This is obtained from the ineffective crack length against the Fatigue Limit. Next, an equivalent notch depth is proposed to replace a rough profile to a smooth profile with a notch. To calculate the stress concentration of the notch and to determine the equivalent notch depth, an exact solution is given for a problem of an infinite plate with a complex profile under tension. The solution is obtained with the complex variable method. Finally, a method to predict the Fatigue Limit reliability is discussed. The Linear Notch Mechanics and \(\sqrt{area}\) parameter model is used to predict the Fatigue Limit of a smooth profile with a notch, and then the Fatigue Limit reliability is estimated with the Fatigue Limit of many simulated surfaces. Moreover, rotating bending Fatigue tests of 0.1% carbon steel with a complex surface are carried out. The experimental Fatigue Limit data is compared with the present estimated value. As results, the validity of the present method is examined.
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Fatigue Limit investigation of 6061 t6 aluminum alloy in giga cycle regime
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Yoshimasa Takahashi, Hiroaki Yoshitake, Ryota Nakamichi, Takuya Wada, Masanori Takuma, Takahiro Shikama, Hiroshi NoguchiAbstract:Abstract In order to investigate the Fatigue Limit micro-mechanism of a precipitation-hardened Al–Mg–Si alloy (6061-T6), the alloy was subjected to very-high-cycle Fatigue (VHCF) of over 109 cycles by an ultrasonic Fatigue method. Two kinds of specimens, one with smooth surface and the other with a small artificial hole on the surface, were compared. The smooth specimens showed no distinct Fatigue Limit. Conversely, the holed specimens showed clear Fatigue Limit which had been generally deemed to be absent in non-ferrous alloys. In addition to the conventional Fatigue crack growth (FCG) observation by replica technique, metallographically critical analyses by electron backscattered diffraction (EBSD) and cross-sectional focused ion beam (FIB) were conducted to reveal the micro-plasticity associated with FCG. It was found that the Fatigue life of smooth specimens at low stress amplitude was controlled by an unstoppable FCG mechanism mediated by persistent slip bands (PSBs). On the other hand, the emergence of distinct Fatigue Limit in holed specimens was attributed to a non-propagating crack having mode I characteristics in essence. No coaxing effect was, however, confirmed for such non-propagating cracks. The above results, which were somewhat different from previous ones obtained by rotating bending under normal frequency, were discussed in terms of both metallurgical and mechanical points of view.
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evaluation of Fatigue Limit characteristics of lamellar pearlitic steel in consideration of microstructure
Journal of The Society of Materials Science Japan, 2011Co-Authors: Shigeru Hamada, Yuu Sakoda, Daisuke Sasaki, Masaharu Ueda, Hiroshi NoguchiAbstract:In this study, tensile and Fatigue tests were performed to evaluate the Fatigue Limit of lamellar pearlitic steel used for manufacturing railroad rail. The Fatigue ratio of lamellar pearlitic steel was lower than that of general steels, the reason for which is unknown. Fatigue cracks initiated in pearlitic steel at a very early stage of the Fatigue test. Then, it was speculated that the steel should be treated as that with initial defects. In order to determine the initial defect size in the ultra-low cycle Fatigue test, tensile tests were performed. The tensile test results clarified that the crack initiation size depends on the crystal structure. In order to predict the Fatigue Limit of the pearlitic steel, the prediction method proposed by Murakami was applied to the steel. The measured defect sizes were applied to the prediction method, and Fatigue tests were performed. The predicted Fatigue Limit and the test results were in good agreement. In addition, in order to evaluate the crystal structure at the location of the Fatigue crack initiation, electron backscatter diffraction pattern (EBSD) analyses were performed. The analysis results revealed that the crack initiation depends on the pearlite block. Then, we concluded that the Fatigue Limit of pearlitic steel can be predicted by Murakami's method and the defect size is pearlite block size. Then, decreasing the pearlite block size would cause an improvement in the Fatigue Limit of the pearlitic steel.
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effect of prestrain on and prediction of Fatigue Limit in carbon steel
International Journal of Fatigue, 2007Co-Authors: Minwoo Kang, Yuuta Aono, Hiroshi NoguchiAbstract:The effect of prestrain on the Fatigue Limit of 0.1% (annealed) and 0.5% (quenched and tempered) carbon steel was investigated. Formulas for predicting the Fatigue Limit of carbon steels were proposed. The Fatigue Limit of 0.1% carbon steel increased with increasing surface hardness and surface compressive residual stress imposed by prestrain. The Fatigue Limit decreased when precracks were generated on the surface, in spite of a large surface compressive residual stress in the case of 0.5% carbon steel. The precrack, variation of surface hardness and surface residual stress were considered to be parameters applicable in formulas for predicting the Fatigue Limit of prestrained carbon steels. The calculated results of such formulas showed good agreement with the experimental results.
D Lohe - One of the best experts on this subject based on the ideXlab platform.
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increasing the Fatigue Limit of a bearing steel by dynamic strain ageing
International Journal of Fatigue, 2008Co-Authors: Eberhard Kerscher, Karl-heinz Lang, O Vohringer, D LoheAbstract:Dynamic strain ageing processes may increase the Fatigue Limit of steels. To activate these processes, thermomechanical treatments with cyclic loadings at the temperature of the highest effectiveness of dynamic strain ageing can be applied. The treatments increase the dislocation density and change the dislocation structure to a more stable state by immobilisation of mobile dislocations due to locking processes by dissolved carbon atoms and small carbides. The generated dislocation structure requires higher stress amplitudes to induce dislocation movements, and consequently a longer crack initiation period, a lower crack propagation rate and a higher Fatigue Limit at room temperature occur.
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increasing the Fatigue Limit of a high strength bearing steel by thermomechanical treatment
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Eberhard Kerscher, Karl-heinz Lang, D LoheAbstract:High-strength steels have a maximum of the Fatigue Limit at a certain tensile strength. The decrease of the Fatigue Limit at still higher tensile strength can be explained by the failure mechanism of high-strength steels which fail due to crack initiation at inclusions or other internal flaws. To increase the Fatigue Limit two different thermomechanical treatments (TMTs) are applied to the material after classical martensitic hardening and tempering. A TMT results in a decrease of the hardness of about 10%. Different cyclic loading during the TMT can either reduce or increase the Fatigue Limit. In order to describe and compare the different treatments an evaluation of the stress intensity factors arising at the critical inclusions was carried out. To take into account different numbers of cycles to failure in the calculation a modification of the calculation of the stress intensity factor according to Murakami was successfully developed.
