تحليل عددي ميدان تنش پسماند ناشي از فرآيند ليزر كوبي الياژ تيتانيوم Ti - 6AL

چكيده انگليسي :

119 Numerical analysis of residual stress field induced by laser shock peening of Titanium alloy Ti 6Al 4V Hamid Reza Safian Safian127@gmail com Date of Submission 2015 08 15 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Mohsen Badrossamay mohsen badrossamay@cc iut ac irEhsan Foroozmehr eforoozmehr@cc iut ac irAbstractLaser shock peening LSP is a surface treatment process that is performed to improve the fatigue life ofcomponents In this process by applying a pulse of laser energy and shock wave propagation in the component a compressive residual stress field in the metal piece is created The main task of LSP is creating compressiveresidual stress and strain due to surface hardening that can improve the mechanical properties such as resistanceto fatigue and corrosion of the metal parts Residual stress distribution in the piece depends on the productionand propagation of the shock wave and its interaction with the part LSP process parameters include themagnitude of the maximum plasma pressure caused by the laser pulse laser pulse width number of impact ateach point and the overlap of different shots This is important to note that improper combination of theseparameters may lead to substantial tensile residual stress that is detrimental to the mechanical performance ofthe component In this study it was tried to determine an appropriate combination of these parameters by usingfinite element simulation of residual stress caused by LSP and validating with experimental results performedin other studies First through a three dimensional finite element model the magnitude and depth of residualstress obtained from the simulation were compared with experimental results and the model was validated Then using an axisymmetric finite element model the residual stresses induced by a circular laser pulse indifferent states of the mentioned parameters were simulated The effect of each process parameters on theproperties of the residual stress field was studied carefully by applying a design of experiment method Theseproperties included maximum compressive residual stress and its depth depth of compressive residual stressfield maximum compressive residual stress on the surface amount of residual stress in the center of collisionarea the maximum tensile stress and its depth The results showed that the laser pulse width had oppositeeffects on the maximum compressive residual stress and the depth of compressive residual stress fields inwhich are the two important characteristics of LSP treatment Although an increase in the laser pulse width ledto a reduction in compressive residual stress its depth increased with laser pulse width increasing The optimalresults for LSP of titanium alloy Ti 6Al 4V occurred with selection of maximum pressure between 5 6 GPa to7 GPa and laser pulse width between 5 ns to 10 ns Increasing the number of shots at each location also couldenhance the depth of the residual stress In addition the effect of the overlap of spots including the overlappercentages of 30 50 and 70 was investigated The results showed that by increasing the beam overlapthe compressive residual stresses was increased and residual stresses on the surface were more uniform Studying the effects of different patterns of linear spiral inward and spiral outward showed that the spiralinward pattern created the most magnitude of compressive residual stress while the pattern of treatment hadno effect on the depth of compressive residual stress Keywords Laser shock peening compressive residual stress shock waves FEM Ti 6Al 4V

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تحليل عددي ميدان تنش پسماند ناشي از فرآيند ليزر كوبي الياژ تيتانيوم Ti - 6AL - 4V

تنش پسماند فشاري , امواج ضربه اي , روش اجزاء محدود