Mechanical Behavior Prediction Of Friction Stir Welding Based On Crystal Plasticity

Compared with traditional welding,friction stir welding technology has less pollution,and is especially suitable for welding aluminum alloys.With the deepening of experimental and theoretical research,it has been applied to various fields of industrial production,such as aircraft,subway,automobile and others.During the welding process,the micro structure at the welding joint undergoes a series of changes under the effects of the stirring pin.These changes will have a major impact on the macro mechanical properties of the joint.As a result,it is necessary to study the relationship between the development of the micro structure at the welding joint and the macro mechanical properties of the joint.In this paper,based on the basic theory of crystal plasticity,a numerical simulation scheme is established to integrate the temperature,micro structure and the mechanical behavior of the friction stir welding process.This paper takes 6005A-T6 aluminum alloy as the research object and simulates the welding process at different welding speeds based on the numerical simulation method of moving heat source.The temperature field of the weld nugget?WNZ?at the joint position at different welding speeds is extracted,and the temperature history at different welding speeds are compared and analyzed.In this paper,the temperature distribution history of the nugget zone at different welding speeds calculated based on the mobile heat source method is applied to the simulation of the micro structure evolution.The average grain size and grain morphology characteristics were compared with the results of grain growth at different welding speeds.At the same time,by using the script language of the finite element software HYPERMESH to extract the geometric information of the poly-crystals calculated by the Monte Carlo method,the Monte Carlo poly-crystalline geometric model is converted into a finite element model,which gives an end to the entire conversion process.In this paper,based on the basic theory of crystal plastic finite element method,the mechanical properties of the weld nugget area at different welding speeds are calculated by using UMAT in the finite element software ABAQUS.The yield strength value obtained by numerical simulation is compared with the experimental value to verify the calculation results in this paper.The stress distribution characteristics of the nugget zone at different welding speeds are analyzed,and the actuation of different slip systems at the same welding speed is compared.The results show that the degree of activation of the slip system in different grains is different,and the degree of activation of different slip systems in the same grain is also different,and the ununiformity of stress and strain distribution is explained.In this paper,a welding speed of 200 mm·min^-1 is used as an example to give Monte Carlo poly-crystals four different initial orientation values.On the condition that other parameters are consistent,the calculation results of the four sets of initial orientations are compared and analyzed.The results show that the calculation of 60 grains in this paper can better express the macroscopic uniformity characteristics of poly-crystals.