大口径薄壁Ti−6Al−4V管材数控温弯中不同应变速率和温度下的Johnson−Cook本构模型

摘要

大口径薄壁Ti?6Al?4V管是航空航天等高端制造领域亟需的典型轻量化高性能构件,数控温弯能够有效实现大口径Ti?6Al?4V管的精确成形.由于数控温弯工艺过程是多场耦合复杂变形过程,建立其材料本构模型并实现全过程有限元模拟是亟待解决的瓶颈技术.利用管材单向拉伸实验,结合温弯工艺参数变化,研究温度在25～600°C和应变速率在0.00067～0.1 s?1情况下Ti?6Al?4V管的力学性能.考虑非线性硬化率和应变的交互作用,建立了修正的Johnson?Cook本构模型,并根据实验数据对相关修正参数进行了拟合.将该模型应用于温弯模拟中可发现,修正的JC模型与传统的模型相比,可降低最大误差90％,并且可以有效预测管材断裂、起皱等成形缺陷发生的位置,为大口径薄壁Ti?6Al?4V管数控温弯成形极限和工艺优化奠定基础.%Numerical control (NC) warm bending is a proven strategy to form the large diameter thin-walled (LDTW) Ti?6Al?4V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti?6Al?4V tube within wide ranges of temperatures (25?600 °C) and strain rates (0.00067?0.1 s?1). Moreover, a modified Johnson?Cook (JC) model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90％. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti?6Al?4V tubes.