Three different stress states of the combination of tensile（t） stress and compressive（c） stress,t t,t c and t c c,exist in the deformed commercially pure titanium（CP-Ti） sheet during cold drawing-bulging.The textures and microstructures in the different stress state regions were investigated by means of XRD and TEM analysis.Similar development of texture and microstructure is achieved with less thickness strain under multiaxial stresses in drawing-bulging than in cold rolling.The results show that texture and microstructure are much sensitive to multiaxial stresses.Twinning is more easily activated under compressive stress than tensile stress.Prism a slip is heavily affected by tensile stress,resulting in a remarkable change of the intensity of（0°,35°,0°） texture,while pyramidal c＋a slip,forming（20°,35°,30°） texture,weakens with the increase of thickness strain in spite of stress state.
In this paper,the effects of hardening exponent,yield strength and elastic modulus on the deformability of near hemispherical shells are investigated by means of finite element method and orthogonal experiment design.The largest eccentric angle during the deformation process and thickness reduction after the deformation are introduced to estimate the deformability quantitatively according to the deformation characteristics of near hemispherical shells.The results indicate that the hardening exponent is the most influential parameter,followed by elastic modulus and yield strength.The shell exhibits good deformability when the hardening exponent and elastic modulus are in the range of 0.1-0.125 and 70-108 GPa,respectively.
The asymmetric deformation and eccentricity problems of near hemispherical diaphragm under the uniform surface load are quantitatively characterized in the paper.The analysis is based on a 3D finite element analysis (FEA) model established according to elastic-plasticity and large displacement nonlinear finite element method.Besides,the deformation experiments are taken to validate the reliability of FEA model which shows that the simulation results are in good agreement with the experimental results.Then,three angle parameters,deflection angle β,circumvolving angle θ and distributing angle γ,are introduced and expressed to characterize the asymmetric deformation and eccentricity quantitatively.According to the angle parameters,the inversion processes of uniform thickness diaphragm and varying thickness diaphragm are calculated respectively.The inversion process of varying thickness diaphragm is much steadier than that of uniform thickness diaphragm.The present results show that the asymmetric deformation process can be characterized by curve of three angle parameters (β,θ,γ) exactly,the degrees of eccentricity can be indicated by the final value of deflection angle and the eccentricity position can be characterized by the final values of the three angle parameters.
The deep drawing of titanium thin-walled surface part was simulated based on a self-developed three-dimensional finite element model. After an investigation on forming rules, a virtual orthogonal experimental design was adopted to determine the significance of processing parameters, such as die radius, blank holder force, and friction coefficient, on the forming process. The distributions of thickness and equivalent plastic strain of the drawn part were evaluated. The results show that die radius has a relative major influence on the deep drawing process, followed by friction coefficient and blank holder force.
GAO Enzhi, LI Hongwei, KOU Hongchao, CHANG Hui, LI Jinshan, and ZHOU Lian State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China
During deep drawing process,the material parameters of blank have a significant effect on the quality of the drawn part and the determination of process parameters. Here,a 3D finite element model is developed for the deep drawing process of a thin-walled hemispheric surface part. Then the influences of material parameters including hardening exponent n,yield stress σs and elastic modulus E on the process are investigated by simulation. The results show that the effects of n and σs on punch force,thickness variation and equivalent strain are more notable. The maximum equivalent plastic strain occurs outside the die corner. However,when the value of n is 0.03 or σs is smaller than 120 MPa,higher equivalent plastic strain occurs at ball top.
