Research On Multi Scale Simulation Of Three Dimensional Hot Stretch Bending Of TC4 Titanium Alloy Profile

The thin-walled titanium alloy three-dimensional bending component has the characteristics of high structural strength,good aerodynamic performance,and smooth geometric modeling,which is an advanced lightweight structure urgently needed in the aerospace field.However,due to the increase of bending dimension,as well as the constraints of large-scale integration and thin-walled complex structure characteristics,the accurate formative method needs to be studied.Therefore,a flexible multi-point three-dimensional hot stretch bending process was developed to realize the three-dimensional bending of titanium alloy profiles.In this process,the electric heating method is used to improve the processing performance of titanium alloy profile,and three-dimensional bending of titanium alloy profile is realized by superposition of horizontal and vertical bending deformation.For the sake of realizing the integrated forming manufacturing of TC4 titanium alloy profile components,the three-dimensional hot stretch bending process of TC4 titanium alloy was simulated by the elastic-plastic finite element method and crystal plastic finite element method based on thermal-mechanical coupling.The forming mechanism of TC4 titanium alloy was studied from the macro scale and mesoscale.Firstly,the quasi-static tensile test of the TC4 titanium alloy sheet was carried out at923k-1023 k,and the effects of temperature and strain rate on its mechanical properties were studied;The results show that TC4 is sensitive to temperature and strain rate under quasi-static condition.SEM and EBSD were used to analyze the microstructure and fracture of the tensile specimens.The results show that the texture weakens significantly and the texture type changes after loading along with different directions at high temperature;The softening mechanism below the transformation temperature is α Mutual harmony β The dynamic recovery and dynamic recrystallization of the phase are very important α The main phase is dynamic recovery;Due to the anisotropic behavior,the fracture mechanism at high temperature is not all ductile fracture.Then,according to the stress-strain curve obtained from the experiment,the tensile and three-dimensional stretch bending forming of titanium alloy under thermal-mechanical coupling were simulated by the finite element method.The variation rules of temperature field,stress field,and strain field during deformation are obtained.Based on the law of strain and strain variation,the plastic inhomogeneity of macro deformation of titanium alloy under uniaxial and multiaxial loads is obtained.Finally,based on the crystal information obtained by EBSD,a crystal plastic constitutive model based on the dislocation slip mechanism is established.Based on Voronoi theory,the crystal plastic finite element models of TC4 titanium alloy in tension,two-dimensional bending,and three-dimensional bending were established.The simulation results show that the crystal plastic finite element model can well capture the mesoscopic stress-strain behavior and texture evolution.In the three-dimensional stretch bending process,the loading direction has little effect on the texture type,but has a great effect on the texture strength;Besides,during the loading process,the grains will rotate to change the grain orientation,which makes the start of the slip system different and shows the inhomogeneity of mesoscale deformation.In this paper,the whole process of flexible multi-point three-dimensional hot stretch bending of titanium alloy is studied by multi-scale simulation.It provides a theoretical basis for the subsequent three-dimensional hot stretch bending forming integrated manufacturing of titanium alloy.