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چكيده انگليسي :

Numerical implementation of high strain rate constitutive model for simulation of cold spray process Saeed Rahmati Saeed rahmati@me iut ac ir 15th September 2013 Department of Mechanics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Abbas ghaei ghaei@cc iut ac ir Abstract Cold spray is a relatively modern process used for coating and producing new stuff In this process the solid particles are accelerated to the substrate using a low temperature supersonic gas flow The particles possess a large kinetic energy due to their high velocity As a result both particles and substrate go through a severely large deformation in this process which causes a strong bonding with them The rate of deformation in cold spray process spans a wide range i e usually from 109 to zero s 1 The experimental study of this process is generally very difficult as the deformation occurs in a very short period of time and also in very small region Therefore numerical simulation of the process can provide insight into this process Many numerical studies have been carried out in the literature in order to study this process in more depth Despite the inability of Johnson Cook plasticity model in prediction of material behavior at high strain rates it is the model that has been frequently used in simulation of cold spray Therefore this research was devoted to compare the performance of different material models in the simulation of cold spray process Six different material models appropriate for high strain rate plasticity were implemented into ABAQUS commercial code via VUHARD user subroutine Then the subroutines were used to simulate the cold spray process for pure copper The simulations were carried out using two methods a conventional Lagrangian elements FEM and b smoothed particle hydrodynamics method SPH The simulation results were compared with the previously published experimental data The results of this study showed that the material model had a considerable effect on the predicted deformed shape The results of FEM showed that the Johnson Cook model underestimated the flow stress at both of high strain rate and large plastic strain and therefore over predicts the particles deformation in the cold spray process Against the Johnson Cook model some models overestimated the flow stress at high strain rate or large plastic strain i e Gao Zhang Voyiadjis Abed and Modified Zerilli Armstrong models The PTW model predicts the flow stress fairly accurately at both of high strain rates and large plastic strain and therefore predicts the deformation in the cold spray process fairly accurately Also the jetting phenomenon that is very important in bonding mechanism in cold spray process is only captured by some models i e Johnson Cook PTW and Modified Khan Huang Liang models Comparison of results of FEM and SPH method generally shows that results of both methods are almost similar In the SPH method particles do not rebound after impacting and adhere onto the substrate this property may arise from the powerful capability of the SPH method for capturing the interfacial features Keywords Cold Spray Process Numerical Simulation Finite element method Smooth particles hydrodynamics Material model High Strain Rate PDF created with pdfFactory trial version www pdffactory com

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پياده سازي عددي يك مدل براي نرخ كرنش هاي بالا به منظور شبيه سازي فرآيند اسپري سرد

شبيه سازي المان محدود , شبيه سازي هيدروديناميك ذرات هموار , مدل ماده