Ti-4Al-1.5Mn合金高温应力松弛本构模型及应用验证

Material Characterization and Validation for Stress Relaxation of Ti-4Al-1.5Mn Alloy at High Temperature

摘要:

应力松弛是热校形等精确成形工艺中的关键阶段。在松驰过程中,零件保持变形后的贴模状态一定时间,随着时间的推移零件内部应力逐渐减小。松弛过程的材料性能及本构模型研究是这些工艺的的基础性关键问题。本文研究了Ti-4Al-1.5Mn合金在500至700℃的应力松弛特性,首先在蠕变试验机上开展了该合金500℃、600℃和700℃条件下的松弛试验,基于松弛数据分别建了双曲正弦和时间硬化两类本构模型,并对模型的预测精度进行了预测。随后把两类本构模型应用于ABAQUS软件对板材V形弯曲过程进行了仿真分析。结果表明,应力松弛的影响因素主要有温度和时间,松弛过程可以分为两个阶段,第一阶段应力快速下降,第二阶段缓慢下降并逐渐稳定于松弛极限。双曲正弦和时间硬化模型均可以对松弛过程进行较准确地预测,V形弯曲后回弹结果表明双曲正弦比时间硬化模型具有更高的预测精度。研究结果对利用应力松弛进行精确成形的工艺设计具有指导意义。

Abstract:

Stress relaxation is a critical stage for some accurate forming processes, such as hot sizing. In the relaxation stage, the part keeps the deformed status, meanwhile the internal stress decreases as time increases. Material characterization and constitutive modeling for the stress relaxation behavior are the fundamental issues for these forming processes. The present work focus on the material characterization and validation of relaxation behavior of Ti-4Al-1.5Mn alloy at high temperature. Firstly, constitutive models for the relaxation behavior at 500℃, 600℃ and 700℃ are established based on the stress relaxation tests. Further, the models are applied to finite element software ABAQUS to simulate the influence of stress relaxation on the springback after V-bending. The results show that the stress relaxation is controlled by temperature and relaxation time. The relaxation process can be divided into two stages. In the first stage, the stress decreases fast. In the second stage, the stress decreases slowly. Finally the residual stress decreases to a limit value, which is defined as relaxation limit. Both hyperbolic sine and time hardening model can predict the variation of stress relaxation. The predicted springback shows promising agreement with the corresponding experimental observations. Hyperbolic sine model is more reliable than the time hardening model. The study is of guiding significance for the design of precise forming process by means of relaxation process.