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Rails fracture by the growth of fatigue crack or critical crack is one of the prevalent defects in railway. The rail fracture, failure and analysis of stress should be studied to prevent rail fracture and events. In this paper, new formulation of contact stress for two rolling bodies is presented, and its results are close to the hertz stress formulation. The analysis of stress is done by Finite Element Model (FEM) and it is compared with hertz stress and new stress formulation results. Then, the analysis of stress, fracture, prediction of fracture and path of crack motion in rail and wheel are studied, statically which plays an important role in this field. The methods of analysis of stress theory fracture with numerical and FEM are compared and consequently, it was proved that these approaches have acceptable results compared with other results. So we can rely on these methods and their results. The relation between maximum displacement and maximum stress is presented, and the path of crack growth and fracture is predicted. To analyze the pressure of collection of the wheel and rail instead of elliptical contact surface, quadrant of elliptical contact surface is assumed. With this assumption, acceptable results will be attained. ©2011 Academic Journals. Source


Monfared V.,Islamic Azad University at Zanjan | Mondali M.,Islamic Azad University at Tehran
Materials and Design | Year: 2014

In this research work, semi-analytical method (SAM) is presented to predict composite creep strain rate and quasi shear-lag (QSL) formulation directly, as well as, finite element method (FEM) is employed for predicting partial creep debonding at the interface in steady state creep of short fiber composites under tensile axial stress. Also, new formulation QSL is introduced to obtain the average axial stress in fiber which its results are similar to the results of shear lag (SL) model. Then, it is shown that FEM can approximately predict the partial debonding in some regions of the interface. As a result, interfacial debonding can be caused by high tensile axial and circumferential stresses, high shear and equivalent stresses, and low compressive radial stresses with considering stress concentration. The results obtained from SAM are in good agreement with the available experimental results. Finally, it is concluded that FEM simulation can be useful for predicting some defects such as interfacial debonding and also better designing the fibrous composites. © 2013 Elsevier Ltd. Source


Stress behavior in short fiber composites under axial tensile stress is predicted based on well-behaved displacement rates in the steady state creep using imaginary fiber technique. This analysis is performed without using shear-lag model and other complex theories in non-reinforced regions of the short fiber composites. Direct analytical method (DAM) is presented to obtain the composite creep strain rate and stress behavior. Because of many applications of silicon carbide fiber SiC/Al6061 composites, stress analysis of this composite is done. Good agreements are found between the obtained present analytical and finite element method (FEM) results. Some important applications of the present comprehensive method are in the fields of the safe composite design and control of creeping composites in order to prevent the creep rupture. Also, present method is simple and accurate, unlike costly, difficult and time-consuming experimental methods. ©2015 Elsevier Ltd. All rights reserved. Source


Tabari H.,Islamic Azad University at Amol | Aghajanloo M.-B.,Islamic Azad University at Zanjan
International Journal of Climatology | Year: 2013

The knowledge of aridity is needed to explain landscape characteristics and the rational utilization of water resources. With global warming, an increase in aridity is expected for many parts of the world. This study was undertaken to analyse monthly and annual aridity index (IA), utilizing ratio of precipitation (P) over reference evapotranspiration (ETo), at ten stations located in critical agricultural regions in Iran. The Kendall and Spearman tests with considering serial correlation effect were used for analysis. An increase in aridity, as the P/ETo index decreased, was found during the study period, and the increase was more obvious in the semi-arid region of Iran than in the humid region. The increase of aridity was caused by the concurrent occurrences of negative P trends and positive ETo trends. The results indicated the lowest numbers of the negative IA trends in the July series and the highest numbers in the January, February and March series. According to the Theil-Sen's estimator, the annual P of the semi-arid and humid regions decreased at the average rates of (-)22.87 and (-)6.24 mm year-1 per decade respectively, whereas the annual ETo values in the semi-arid and humid regions increased by (+)11.42 and (+)6.82 mm year-1 per decade, respectively. © 2012 Royal Meteorological Society. Source


Monfared V.,Islamic Azad University at Zanjan
Composites Science and Technology | Year: 2015

A novel analytical method is developed for predicting steady state creep of short fiber composites using shear-lag theory, imaginary fiber technique and polynomial displacement functions. Also, this method employs equilibrium and constitutive equations. Polynomial displacement method (PDM) is a new insight for analysis of plasticity and elasticity problems which can be used as a simple, exact and general method. PDM is more accurate than the available methods. Important novelties of the PDM are determination of unknowns such as shear stresses and displacement rates on top of the fiber analytically. In this paper, all unknowns are obtained by well-behaved polynomial displacement functions. These functions satisfy incompressibility and boundary conditions. In spite of the previous researches, strain rates and stresses are analytically obtained by PDM without non-analytical assumptions. Also, suitable agreements are found among present analytical method, numerical (FEM) and available published results. © 2014 Elsevier Ltd. Source

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