| Due to its excellent properties and good formability,aluminum alloy profile is commonly used in the bending beam structures of high-speed rail trains.During the bending forming process,large deformations can cause roughening of the profile surface.Severe roughening can lead to orange peel defects,which results in material failure.At present,most research on surface roughness is based on sheet metal forming theory,which cannot be directly applied to profiles with complex cross-sectional shapes.There is also relatively little research on the critical conditions for the occurrence of orange peel defects.In this paper,the free surface of the belly plate of the 6005 A aluminum alloy profile is taken as the research object,and a crystal plasticity finite element model is established to explore the evolution law of roughness under the influence of different bending forming parameters and the critical conditions for the occurrence of orange peel defects,to predict and prevent the formation of orange peel during the bending forming process.The main research work of this paper is as follows.(1).Uniaxial tensile tests and EBSD testing were performed on the surface of the web plate of the 6005 A aluminum alloy profile to obtain its basic mechanical properties,grain size information,grain shape,and orientation distribution.Uniaxial tensile tests were also performed on trapezoidal specimens,and combined with Argus strain analysis and laser confocal microscopy roughness analysis,continuous strain gradients and roughness gradients were obtained.Based on the above experimental data,a crystal plasticity finite element model was established,and the model calculation data after size effect compensation was consistent with the experimental results.(2).A comparative analysis of the stress characteristics of the profiled plate in different bending processes was conducted to establish a roughness evolution finite element model and study the evolution of roughness under biaxial normal stress,shear stress,and initial morphology effects.The results show that the roughness development under different types of biaxial strain differs,and the equivalent stress is not sufficient as a unified standard for predicting orange peel defects.The contribution of shear deformation to roughening varies with different directions due to the anisotropy of orientation and grain shape.The roughness development rate under pure shear state is lower than that under normal stress.The representative volume element model with initial roughness has a reduced roughening rate,but the final roughness result is still higher than that of a smooth surface model.(3).The orientation matrix of surface grains was calculated by extracting the state variables from simulation results,and the orientation analysis of surface grains during deformation was conducted.As the deformation proceeded,the Cube texture component peak disappeared,and the Goss texture component peak weakened,while a weaker Brass texture appeared,and the maximum peak intensity decreased by 60%.The results showed that the normal strain had a significant influence on the evolution of surface texture orientation in the 6005 A aluminum alloy,and controlling the normal strain could slow down the occurrence of orange peel defects,which provided a theoretical basis for judging the generation of orange peel defects through critical biaxial strains.(4).A macro finite element model for aluminum alloy profile bending was established,and the surface strain distribution during press bending and roll bending was simulated and analyzed.Based on this,three typical deformation paths were established.By analyzing the simulation results,the numerical evolution relationship between roughness and biaxial strain,as well as the critical biaxial strain for orange peel prediction,were obtained for predicting the generation of orange peel.Based on this,the generation of orange peel in stretching bending,press bending,and roll bending was predicted,and the results showed that the forming process with less displacement constraint was prone to produce orange peel defects. |
