Thermo-Mechanical Coupling Analysis Of Dual Laser Beam Bilateral Welding For Al-Li Alloy Skin-Stringer Structure

With the rapid development of modern space technology,the advanced materials and structures of aerospace craft are extremely expected.Progressive and efficient joining technology is one of the most important directions of manufacturing technology,which is used in skin stringer panel structure of aerospace crafts.In recent years,with the rapid development of laser power,laser welding is widely used in the joining of aluminum alloy structure.At present,it is an urgent problem to be solved that Al-Li alloy skin-stringer structures in aerospace craft are successfully welded by dual laser beam bilateral synchronous welding(DLBSW)technology.Based on this background,the study on DLBSW of skin-stringer structure for aerospace craft panel is carried out by experiment and thermo-mechanical coupling simulation.Firstly,the welding process experiment of 5A90 Al-Li alloy skin stringer structure test piece is performed.The macroscopic morphology and micro-structure of welded joints are analyzed.The hardness and tensile properties of welded joints are tested.Moreover,the micro-morphology and fracture mechanism is analyzed by scanning electron microscope(SEM).And the composition of fracture area is analyzed by energy dispersive spectrometer(EDS).Secondly,based on the real dimension of the aerospace craft panel skin-stringer structure,the three-dimensional geometric models of single stringer test piece,typical component(three stringers)and simulated component(seven stringers)are established.Then,the finite element mesh models of the three kinds of structural components are established by using the non-uniform transition mesh technology.The characteristics of double laser beam welding are fully investigated.And the heat source subroutine is compiled to realize the heat source loading of thermo-mechanical coupling simulation.Moreover,the boundary condition and welding path are loaded by completely considering the weld experiment condition.Thirdly,the temperature field simulation of single stringer specimen is carried out by separately using “Gauss surface + cone” hybrid heat source model and “Gauss surface + cylinder” hybrid heat source model.And the simulation results of two different heat source models are compared.The simulation results show that the thermal field using “Gauss surface + cylinder” hybrid heat source model coincide well with the actual welding results.Based on the comparative results,the stress and deformation simulation and experimental verification of single stringer specimen are carried out.The analysis shows that the simulation results of stress and deformation of single stringer specimen are ingood agreement with the experimental results.Finally,based on the optimal welding process parameters obtained from the experiment and simulation of single stringer test piece,the thermo-mechanical coupling simulations of typical component and simulation component in different welding sequence are implemented.The simulation results show that the welding residual stress and post-welding deformation are minimum when the outside symmetrical welding sequence "132" is used for typical component.When the cross welding sequence "1537462" is adopted,the post-weld deformation of the simulation component can be effectively reduced.