镍钛形状记忆合金管滚珠热旋压成形数值模拟

Numerical simulation of hot ball spinning of NiTi shape memory alloy tube

为了获得高性能、高质量的镍钛形状记忆合金薄壁管,尝试采用滚珠热旋压方法进行镍钛形状记忆合金管的成形.通过采用刚粘塑性有限元法对镍钛形状记忆合金管进行滚珠热旋压成形模拟,获得了镍钛形状记忆合金管坯在不同初始温度下的温度场、应力场和应变场,并进行了旋压载荷的预测.模拟结果表明,旋压件主变形区的温升可达100℃以上,故不宜选择太高的旋压初始温度;旋压成形时主变形区处于三向压应力状态,这将有利于提高材料的塑性,从而实现更大程度的塑性变形;主变形区的等效应力和等效应变数值均由外壁到内壁逐渐减小,说明旋压成形时管坯的外壁比内壁更容易满足塑性屈服准则;随着旋压温度的升高,各方向的旋压载荷均呈下降趋势,轴向载荷远远小于径向载荷和切向载荷.

Hot ball spinning was used to manufacture nickel-titanium shape memory alloy（NiTi SMA） tube with high performance and high quality. The hot ball spinning of the NiTi SMA tube was simulated by means of rigid- viscoplastic finite element method （FEM）, and consequently the temperature field, the stress field, the strain field and the spinning load prediction of NiTi SMA tube under ball spinning at the different initial temperatures were obtained. The simulation results show that the temperature rise is over 100~C in the principal deformation zone of the spun part, and too high initial temperature should not be selected during spinning. In the process of spinning, the principal deformation zone is in a three-dimensional compressive stress state, which contributes to enhancing the plasticity of the metal material and thus realizes greater plastic deformation degree. Both the equivalent stress and the equivalent strain in the principal deformation zone decrease gradually from the outer wall to the inner wall, which indicates that the outer wall of the NiTi SMA tube is easier to meet the plastic yield criterion than the inner wall. The spinning loads in all directions exhibit a decreasing trend with the increase in the spinning temperature, and the spinning load in the axial direction is far less than that in the radial and tangential directions.