Atieh Moridi - Academia.edu (original) (raw)

Papers by Atieh Moridi

Procedia Engineering, 2011

Cast aluminium-silicon alloy, A356.0, is widely used in automotive components such as diesel engi... more 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 stressstrain hysteresis loop are validated by an out of phase thermo-mechanical fatigue test. Then, ceramic coating thickness effect on stress distribution of test specimens is investigated. Different thicknesses from 300 to 800 microns of top coat and also roughness of the interfaces are simulated to get best stress gradient which can cause an improvement of fatigue life. Studying realistic interface roughness shows the critical area of tensile stress which results in crack initiation. Furthermore increasing TC thickness results in stress growth.

Materials and Design, 2012

An offshore structure is exposed to environmental loading and cyclic stress variations throughout... more An offshore structure is exposed to environmental loading and cyclic stress variations throughout its life. This would result in the possibility of fatigue cracking in its members. Cracks in these structures usually initiate around welded areas, then grow progressively from the heat-affected zone to base metal through the thickness of the tubular members. Therefore, fatigue life improvement of offshore structures is of great importance. In this paper, structural analysis of an offshore platform is carried out and the critical joint is specified. The welding process is simulated and the residual stresses due to the welding are determined. Experimental residual stress measurement is carried out and is compared with the simulation result. The simulation results show that the heat affected zone (HAZ) is formed in whole thickness of the brace at weld toe location and approximately half thickness of the chord. The fatigue life of the welded tubular X-joints of offshore structure is investigated experimentally. Furthermore, some joints are shot peened and the effect of shot peening on fatigue life of these joints is explored. The results of experiment show that the fatigue life of shot peened tubular joint is about twice of the original tubular joint. Cracks are initiated in all cases at weld toe. Also a crack on chord branch of joints under fatigue test is observed.

Surface and Coatings Technology, 2014

Cast aluminium-silicon alloy, A356.0, is widely used in automotive and aerospace industries becau... more 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 simulated to get best stress gradient. Results show that increasing top coat thickness causes stress increase. The realistic interface model is useful for identifying critical areas in stress development. Two important factors having considerable effect on development of high stress in TBC, are the severity of undulations relating to amplitude and wavelength of interface waves; and the thickness of BC layer relating to mutual positioning of either interfaces. However the realistic model has some limitations including long calculation time and difficulties of generating a suitable mesh. To diminish these limitations, after recognizing critical area, in second stage of the study, a periodic unit cell is used instead . Eight models considering different mutual positioning of interfacial asperities along with different penetration in adjoining layers are simulated and compared. Results show that detachment of the thermal barrier coating system from substrate is more probable Results show that IP positioning of mutual waves produce more severe stress but contour pattern is less likely to promote crack propagation.

International Journal of Surface Science and Engineering, 2012

ABSTRACT Ceramic thermal barrier coatings are applied on gas turbines and diesel engine component... more 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 thickness of 350 µm. The results of sensitivity analysis show that target functions including maximum bending force, stress and deflection of specimens are optimised at a feed rate of 30 gr/min and nozzle distance of 80 mm.

International Journal of Fatigue, 2014

Fatigue strength of mechanical components can be greatly enhanced by generating compressive resid... more Fatigue strength of mechanical components can be greatly enhanced by generating compressive residual stress, increasing the hardness and reducing the grain size. It is well known that while the use of mechanical treatments is able to generate an effective field of compressive residual stresses and, if severe parameters are used, to cause grain refinement, thermochemical treatments are able to increase the surface hardness. This justifies the interest in developing combined treatments, able to achieve all the just mentioned factors.

Applied Surface Science, 2013

Cold spray is a coating process in which bonding is obtained when the impact velocity of small pa... more Cold spray is a coating process in which bonding is obtained when the impact velocity of small particles exceeds a critical value called critical velocity (CV) but it is less than an upper limit beyond which erosion happens. The success of the cold spray process mainly depends on the correct choice of the process velocity which should be set to be between CV and erosion velocity (EV), that are influenced by many parameters. This justifies the interest of many researchers to define models for the CV assessments. In the present work, we propose a new model, combination of numerical and analytical solutions, to calculate not only the CV but also EV. Compared with previous works, porosity of particles and adherence phenomena between particle and the substrate have been taken into account as a novelty. Results of the proposed approach have been compared with experimental data and good agreement was found. Finally, based on the procedure results, a representative equation was established for calculating critical and erosion velocities as a function of particle porosity, diameter and temperature for Cu and stainless steel 316L particles.

Procedia Engineering, 2011

Cast aluminium-silicon alloy, A356.0, is widely used in automotive components such as diesel engi... more 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 stressstrain hysteresis loop are validated by an out of phase thermo-mechanical fatigue test. Then, ceramic coating thickness effect on stress distribution of test specimens is investigated. Different thicknesses from 300 to 800 microns of top coat and also roughness of the interfaces are simulated to get best stress gradient which can cause an improvement of fatigue life. Studying realistic interface roughness shows the critical area of tensile stress which results in crack initiation. Furthermore increasing TC thickness results in stress growth.

Materials and Design, 2012

An offshore structure is exposed to environmental loading and cyclic stress variations throughout... more An offshore structure is exposed to environmental loading and cyclic stress variations throughout its life. This would result in the possibility of fatigue cracking in its members. Cracks in these structures usually initiate around welded areas, then grow progressively from the heat-affected zone to base metal through the thickness of the tubular members. Therefore, fatigue life improvement of offshore structures is of great importance. In this paper, structural analysis of an offshore platform is carried out and the critical joint is specified. The welding process is simulated and the residual stresses due to the welding are determined. Experimental residual stress measurement is carried out and is compared with the simulation result. The simulation results show that the heat affected zone (HAZ) is formed in whole thickness of the brace at weld toe location and approximately half thickness of the chord. The fatigue life of the welded tubular X-joints of offshore structure is investigated experimentally. Furthermore, some joints are shot peened and the effect of shot peening on fatigue life of these joints is explored. The results of experiment show that the fatigue life of shot peened tubular joint is about twice of the original tubular joint. Cracks are initiated in all cases at weld toe. Also a crack on chord branch of joints under fatigue test is observed.

Surface and Coatings Technology, 2014

Cast aluminium-silicon alloy, A356.0, is widely used in automotive and aerospace industries becau... more 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 simulated to get best stress gradient. Results show that increasing top coat thickness causes stress increase. The realistic interface model is useful for identifying critical areas in stress development. Two important factors having considerable effect on development of high stress in TBC, are the severity of undulations relating to amplitude and wavelength of interface waves; and the thickness of BC layer relating to mutual positioning of either interfaces. However the realistic model has some limitations including long calculation time and difficulties of generating a suitable mesh. To diminish these limitations, after recognizing critical area, in second stage of the study, a periodic unit cell is used instead . Eight models considering different mutual positioning of interfacial asperities along with different penetration in adjoining layers are simulated and compared. Results show that detachment of the thermal barrier coating system from substrate is more probable Results show that IP positioning of mutual waves produce more severe stress but contour pattern is less likely to promote crack propagation.

International Journal of Surface Science and Engineering, 2012

ABSTRACT Ceramic thermal barrier coatings are applied on gas turbines and diesel engine component... more 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 thickness of 350 µm. The results of sensitivity analysis show that target functions including maximum bending force, stress and deflection of specimens are optimised at a feed rate of 30 gr/min and nozzle distance of 80 mm.

International Journal of Fatigue, 2014

Fatigue strength of mechanical components can be greatly enhanced by generating compressive resid... more Fatigue strength of mechanical components can be greatly enhanced by generating compressive residual stress, increasing the hardness and reducing the grain size. It is well known that while the use of mechanical treatments is able to generate an effective field of compressive residual stresses and, if severe parameters are used, to cause grain refinement, thermochemical treatments are able to increase the surface hardness. This justifies the interest in developing combined treatments, able to achieve all the just mentioned factors.

Applied Surface Science, 2013

Cold spray is a coating process in which bonding is obtained when the impact velocity of small pa... more Cold spray is a coating process in which bonding is obtained when the impact velocity of small particles exceeds a critical value called critical velocity (CV) but it is less than an upper limit beyond which erosion happens. The success of the cold spray process mainly depends on the correct choice of the process velocity which should be set to be between CV and erosion velocity (EV), that are influenced by many parameters. This justifies the interest of many researchers to define models for the CV assessments. In the present work, we propose a new model, combination of numerical and analytical solutions, to calculate not only the CV but also EV. Compared with previous works, porosity of particles and adherence phenomena between particle and the substrate have been taken into account as a novelty. Results of the proposed approach have been compared with experimental data and good agreement was found. Finally, based on the procedure results, a representative equation was established for calculating critical and erosion velocities as a function of particle porosity, diameter and temperature for Cu and stainless steel 316L particles.