Design of RT Equal Channel Angular Pressing Pure Titanium Workpiece by Finite Element Simulation

摘要:

为了优化室温下等通道转角挤压纯钛工件的几何形状，采用三维有限元软件模拟了纯钛工件的变形行为。通过对比分析工件形状和尺寸对损伤因子、挤压力以及剪切带处应变速率分布等参数的影响，获得了工件最佳几何形状。仿真结果表明，方条形工件的损伤因子大于圆棒型工件，且高于纯钛材料的临界损伤因子，表明方条形工件不利于变形，易产生表面裂纹。3D模拟结果表明，直径为15 mm的圆棒型工件具有最小的损伤因子，适中的挤压载荷以及相对均匀的应变分布。依据仿真结果提供的最佳工件，即直径为15 mm的圆棒型工件，室温下成功挤压出直径15 mm的纯钛圆棒。挤压后样品截面上硬度分布均匀，与3D仿真所预示的均匀应变分布相一致。

Abstract:

In order to investigate the optimal workpiece geometry of pure Ti extruded by equal channel angular pressing (ECAP) at room temperature, deformation behaviors of Ti billets were studied by means of three-dimensional (3D) finite element simulation. The optimal dimensions of pure Ti billets have been obtained by analyzing the influences of workpiece shapes and sizes on damage factor, pressing force, and strain rate distribution at the shearing band. The analytical results show that the square billet exhibits a much larger damage factor than the round billet, and also than the critical damage value of pure Ti materials, which suggests that the square billet is hard to make deformation and prone to trigger surface cracks. The 3D model reveals that the round billet with a diameter of 15 mm is optimal due to the smallest damage factor, proper pressing load and relatively homogeneous strain distribution. Under the optimal workpiece geometry according to numerical simulation results, ECAP experiment of the pure Ti round billet with a diameter of 15 mm can be successfully processed at room temperature. Additionally, hardness distribution of the as-ECAPed Ti rod is homogeneous at cross-section, which is consistent with the prediction of uniform strain distribution by 3D simulation.