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Numerical simulation of induction hardening of torsion bar
, Article Proceedings of the World Congress on Engineering 2011, WCE 2011, 6 July 2011 through 8 July 2011 ; Volume 3 , July , 2011 , Pages 2080-2083 ; 9789881925152 (ISBN) ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is to compare the experimental residual stress fields measured by X-ray diffraction with those predicted from finite element modeling of the whole induction surface hardening process. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the fatigue loading, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress distribution and optimize the process,...
Side effects of shot peening on fatigue crack initiation life
, Article International Journal of Engineering, Transactions A: Basics ; Volume 24, Issue 3 , 2011 , Pages 275-280 ; 17281431 (ISSN) ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
The beneficial effects of shot peening on fatigue life of mechanical components are well known. However, there are some reports in the literature that indicate inappropriate shot peening parameters tend to reduce the fatigue life. It is therefore, the purpose of this study to find a logical quantitative justification for these observations. Using finite element method, a dynamic elasticplastic simulation of shot peening was presented. Effect of shot velocity and size on surface morphology after shot peening were examined. Fatigue crack initiation life calculation of shot peened specimens revealed that beneficial effect of shot peening significantly vanishes in the case of high velocities and...
Numerical investigation of crack orientation in the fretting fatigue of a flat rounded contact
, Article International Journal of Engineering, Transactions B: Applications ; Volume 23, Issue 3-4 , 2010 , Pages 223-232 ; 1728-144X (ISSN) ; Farrahi, G. H ; Sharif University of Technology
Materials and Energy Research Center
2010
Abstract
The growth of slant cracks by fretting fatigue of a half plane in contact with a flat rounded pad was studied. The mode I and mode II stress intensity factors for cracks of various lengths and directions were calculated using the semi-analytical method of the distribution of dislocations, and their cumulative effect on the crack growth was investigated using the strain energy density criterion. The results showed dominance of mode I fracture on crack growth, and based on the observation of strain energy density factor versus crack orientation, the results also suggest that depending on the crack length, the most critical orientations of cracks are at 0° to 20° outward the contact zone. Good...
Modelling of conventional and severe shot peening influence on properties of high carbon steel via artificial neural network
, Article International Journal of Engineering, Transactions B: Applications ; Volume 31, Issue 2 , 2018 , Pages 382-393 ; 1728144X (ISSN) ; Farrahi, G. H ; Sharif University of Technology
Materials and Energy Research Center
2018
Abstract
Shot peening (SP), as one of the severe plastic deformation (SPD) methods is employed for surface modification of the engineering components by improving the metallurgical and mechanical properties. Furthermore, artificial neural network (ANN) has been widely used in different science and engineering problems for predicting and optimizing in the last decade. In the present study, effects of conventional shot peening (CSP) and severe shot peening (SSP) on properties of AISI 1060 high carbon steel were modelled and compared via ANN. In order to networks training, the back propagation (BP) error algorithm is developed and data of experimental tests results are employed. Experimental data...
Reliability assessment of cracked pipes subjected to creep-fatigue loading
, Article Theoretical and Applied Fracture Mechanics ; Volume 104 , 2019 ; 01678442 (ISSN) ; Farrahi, G. H ; Sharif University of Technology
Elsevier B.V
2019
Abstract
The reliability analysis of defective pipes, which operate under creep-fatigue loading conditions has been studied. An austenitic stainless steel pipe containing an axially external semi-elliptical surface crack, subjected to variable internal pressure at elevated temperature has been considered as the benchmark problem. Different parameters in material behavior, geometry parameters, and operational condition have been assumed as random variables in the probabilistic assessments. The reliability of the cracked pipes have been evaluated at various operation times, using different reliability methods. Sensitivity analyses have been conducted to investigate the importance measure of the random...
Effect of severe shot peening on the fatigue life of the laser-cladded Inconel 718 specimens
, Article International Journal of Advanced Manufacturing Technology ; Volume 104, Issue 5-8 , 2019 , Pages 2619-2631 ; 02683768 (ISSN) ; Farrahi, G. H ; Movahhedy, M. R
Springer London
2019
Abstract
This paper presents the influence of the severe shot peening process on the fatigue life of the laser-cladded Inconel 718 specimens which can be employed during refurbishment of components enduring high mechanical cyclic loads such as gas turbine components. In order to quantitatively evaluate the destructive effect of laser cladding on the fatigue endurance, fatigue tests are first performed on the as-received and laser-cladded specimens. Then, microstructural analysis by scanning electron microscope (SEM) is carried out to identify the root causes of the drawback of laser cladding. Moreover, by employing a comprehensive laser-cladding FE analysis considering cyclic plastic material...
Investigation of the effect of pad geometry on flat and rounded fretting fatigue
, Article Scientia Iranica ; Volume 15, Issue 3 , 2008 , Pages 332-339 ; 10263098 (ISSN) ; Farrahi, G. H ; Sharif University of Technology
Sharif University of Technology
2008
Abstract
In this paper, the effect of geometrical parameters on the fretting fatigue of a half-plane in contact with a flat and rounded pad is studied. This is accomplished by calculating and comparing the stress states and stress intensity factors of fretting cracks for a number of pad geometries. The pad geometry is represented by the radius of its rounded corners and the width of its central flat part. The distribution of dislocation method is employed to calculate the stress intensity factors of fretting induced cracks of different lengths for different values of geometrical parameters. The results of this study can be insightful for improving the geometrical design of an aero-engine compressor...
Thermo-mechanical stress analysis of thermal barrier coating system considering thickness and roughness effects
, Article Surface and Coatings Technology ; Vol. 243 , 2014 , pp. 91-99 ; ISSN: 02578972 ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
Abstract
Cast aluminium-silicon alloy, A356.0, is widely used in automotive and aerospace industries because of its outstanding mechanical, physical, and casting properties. Thermal barrier coatings can be applied to combustion chamber to reduce fuel consumption and pollutions and also improve fatigue life of components. The purpose of the present work is to simulate stress distribution of A356.0 under thermo-mechanical cyclic loadings, using a two-layer elastic-visco-plastic model of ABAQUS. The results of stress-strain hysteresis loop are validated by an out of phase thermo-mechanical fatigue test. Different thicknesses from 300 to 800. μm of top coat and also roughness of the interfaces are...
An approach to relate shot peening finite element simulation to the actual coverage
, Article Surface and Coatings Technology ; Vol. 243 , 2014 , pp. 39-45 ; ISSN: 02578972 ; Guagliano, M ; Farrahi, G. H ; Sharif University of Technology
Abstract
Coverage is one of the most important parameters which is always used in practice to characterize a shot peening process. At the same time however, it is the most missing parameter in the finite element simulations of this process. This study aims to relate shot peening simulation to the actual coverage that is developed during the process. Accordingly, two important models from literature are re-simulated and their capability to predict an actual coverage is assessed. Results of this study illustrate that full coverage situation is not captured by these models. Thereafter, a random finite element simulation along with a step by step examination of the treated surface is adopted in order to...
Vibration and buckling analysis of functionally graded beams using reproducing kernel particle method
, Article Scientia Iranica ; Vol. 21, Issue 6 , 2014 , pp. 1896-1906 ; e-ISSN : 23453605 ; Ahmadian, M. T ; Farrahi, G. H ; Sharif University of Technology
Abstract
This paper presents vibration and buckling analysis of functionally graded beams with different boundary conditions, using reproducing kernel particle method (RKPM). Vibration of simple Euler-Bernoulli beam using RKPM is already developed and reported in the literature. Modeling of FGM beams using theoretical method or finite element technique is not evolved with accurate results for power law form of FGM with large power of "n" value so far. Accuracy of the RKPM results is very good and is not sensitive to n value. System of equations of motion is derived using Lagrange's method under the assumption of Euler-Bernoulli beam theory. Boundary conditions of the beam are taken into account using...
Size-dependent energy release rate formulation of notched beams based on a modified couple stress theory
, Article Engineering Fracture Mechanics ; Vol. 116, Issue.1 , 2014 , pp. 80-91 ; ISSN: 0013-7944 ; Kahrobaiyan, M. H ; Farrahi, G. H ; Sharif University of Technology
Abstract
The modified couple stress theory is employed in this paper in order to formulate the size-dependent strain energy release rate of Euler-Bernoulli and Timoshenko notched beams. As a case study, the normalized energy release rate of the aforementioned beams has been developed for three-point bending as a function of the ratio of material length scale parameter to the beam depth. The results of the current model are compared to the experimental data. The good agreement between the present results and the experimental values indicates that the current model can be successfully applied to evaluate size dependent energy release rate of structures
Optimization of air plasma sprayed thermal barrier coating parameters in diesel engine applications
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 11 , 2013 , Pages 3530-3538 ; 10599495 (ISSN) ; Farrahi, G. H ; Moridi, A ; Sharif University of Technology
2013
Abstract
In the present paper, an optimization of thermal barrier coating parameters is performed for diesel engine applications. The substrate is A356.0-T7, a cast aluminum alloy which has a vast application in diesel engines, and the alloy is coated by plasma sprayed ZrO2-8 wt.% Y2O3. Parameters including the feed rate of coating powders, the nozzle distance to specimen surfaces, and the coating thickness are optimized by thermal shock fatigue tests and bending tests. Optimum values of the feed rate and the nozzle distance are 30 g/min and 80 mm, respectively, when the objective is considered as maximizing the bending strength. Thermal shock tests demonstrate that lower thickness of coating layers...
A plasticity model for metals with dependency on all the stress invariants
, Article Journal of Engineering Materials and Technology, Transactions of the ASME ; Volume 135, Issue 1 , 2013 ; 00944289 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2013
Abstract
Recent experiments on metals have shown that all of the stress invariants should be involved in the constitutive description of the material in plasticity. In this paper, a plasticity model for metals is defined for isotropic materials, which is a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. For this purpose, the Drucker-Prager yield criterion is extended by addition of a new term containing the second and the third deviatoric stress invariants. Furthermore for estimating the cyclic behavior, new terms are incorporated into the Chaboche's hardening evolution equation. These modifications are applied by adding new...
An analytical solution for inverse determination of residual stress field
, Article Journal of Solid Mechanics ; Volume 4, Issue 2 , 2012 , Pages 114-127 ; 20083505 (ISSN) ; Farrahi, G. H ; Smith, D. J ; Sharif University of Technology
2012
Abstract
An analytical solution is presented that reconstructs residual stress field from limited and incomplete data. The inverse problem of reconstructing residual stresses is solved using an appropriate form of the airy stress function. This function is chosen to satisfy the stress equilibrium equations together with the boundary conditions for a domain within a convex polygon. The analytical solution is demonstrated by developing a reference solution from which selected "measurement" points are used. An artificial error is then randomly added to "measurement" points for studying the stability of the reconstruction method utilizing Tikhonov- Morozov regularization technique. It is found that there...
Effects of temperature on wear behavior of a plasma sprayed diesel engine cylinder
, Article SAE Technical Papers ; 2012 ; Farrahi, G. H ; Eftekhari, M. R ; Sharif University of Technology
SAE
2012
Abstract
One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate...
Effects of stress invariants and reverse loading on ductile fracture initiation
, Article International Journal of Solids and Structures ; Volume 49, Issue 13 , 2012 , Pages 1541-1556 ; 00207683 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2012
Abstract
Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight...
Optimal experiment design for plasma thermal spray parameters at bending loads
, Article International Journal of Surface Science and Engineering ; Volume 6, Issue 1-2 , 2012 , Pages 3-14 ; 1749785X (ISSN) ; Moridi, A ; Farrahi, G. H ; Sharif University of Technology
2012
Abstract
Ceramic thermal barrier coatings are applied on gas turbines and diesel engine components to protect metals from heat and this enhances the service lifetime by means of a reduction in working temperature. In the present paper, optimisation of plasma thermal spray parameters, including feed rate and nozzle distance from the specimen surface is performed by using the design of experiment method. Due to factorial approach, by considering two parameters with three variation levels, nine experiments of bending test are needed. The base material is cast aluminium alloy, A356.0-T7. The coating layers consist of a bond coat, Ni-Cr-Al-Y with a thickness of 150 μm and a top coat, ZrO2-8wt%Y2O3 with a...
Numerical simulation of thermal barrier coating system under thermo-mechanical loadings
, Article Proceedings of the World Congress on Engineering 2011, WCE 2011, 6 July 2011 through 8 July 2011 ; Volume 3 , July , 2011 , Pages 1959-1964 ; 9789881925152 (ISBN) ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
In the present paper, numerical simulation of thermal barrier coating system under thermo-mechanical loadings is performed, using the finite element method in ABAQUS software. The base material is Aluminum-silicon alloy, A356.0 which is widely used in automotive components such as diesel engine cylinder heads. Thermal barrier coatings (TBCs) are applied to combustion chamber in order to reduce fuel consumption and pollutions and also improve fatigue life of components. The roughness effect of coating layers on stress distribution of test specimens is investigated. Semi-ellipsoid roughness of the interfaces between substrate/bond coat and bond coat/top coat are simulated to get the stress...
Finite element simulation of shot peening coverage with the special attention on surface nanocrystallization
, Article Procedia Engineering, 5 June 2011 through 9 June 2011 ; Volume 10 , 2011 , Pages 2464-2471 ; 18777058 (ISSN) ; Guagliano, M ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
The present study aims to challenge the existing finite element models in terms of one of the most important practical parameters, i.e. coverage. Important models from the literature are re-simulated and their resulted treated surfaces are carefully examined. Result of this study shows that existing finite element models could not reflect the realistic coverage. A variable dimension symmetry cell is developed in order to acquire full coverage and at the same time not increasing the computational cost. This model can successfully simulate the surface nanocrystallization by severe shot peening in which the amount of coverage is much higher than conventional shot peening
Coating thickness and roughness effect on stress distribution of A356.0 under thermo-mechanical loadings
, Article Procedia Engineering, 5 June 2011 through 9 June 2011 ; Volume 10 , June , 2011 , Pages 1372-1377 ; 18777058 (ISSN) ; Azadi, M ; Farrahi, G. H ; Sharif University of Technology
2011
Abstract
Cast aluminium-silicon alloy, A356.0, is widely used in automotive components such as diesel engine cylinder heads and also in aerospace industries because of its outstanding mechanical, physical, and casting properties. Thermal barrier coatings are applied to combustion chamber in order to reduce fuel consumption and pollutions and also improve fatigue life of components. However, studies on behaviour of A356.0 with thermal barrier coating are still rare. The purpose of the present work is to simulate stress distribution of A356.0 under thermo-mechanical cyclic loadings, using a two-layer elastic-visco-plastic model of ABAQUS software. The results of stress-strain hysteresis loop are...