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应力松弛是钛合金在升高温度和加载条件下的一个显著特性,也是热校形和热处理的理论基础。因此研究了一种Ti-6Al-4V钛板在923~1023 K温度范围内、几种应变水平下的拉伸应力松弛行为。结果表明,应力松弛速率随着温度的升高而增加,材料中的残余应力经过一段时间之后趋向应力松弛极限;另外,在相同温度下,不同应力水平的应力松弛极限相同。进而,建立了一种描述应力松弛行为的显式三次延迟函数,本构精度高达97%,可用于工艺设计及理论分析。最后,基于应力松弛和蠕变的关系,提出了一种隐式蠕变型本构方程描述应力松弛行为,并将识别的材料参数输入ABAQUS,数值模拟了Ti-6Al-4V的热应力松弛行为,发现模拟的应力变化规律符合应力松弛曲线,证明了蠕变型本构方程对应力松弛模拟的适用性。
Stress relaxation is a prominent feature of titanium alloys at elevated temperatures and loading conditions, and is also the theoretical basis for thermal alignment and heat treatment. Therefore, the tensile stress relaxation behavior of Ti-6Al-4V titanium plate at several strain levels in the temperature range of 923 ~ 1023 K was studied. The results show that the rate of stress relaxation increases with the increase of temperature, and the residual stress in the material tends to stress relaxation limit after a period of time. In addition, the stress relaxation limits of different stress levels are the same at the same temperature. Furthermore, an explicit third-order delay function describing the stress relaxation behavior is established. The constitutive precision is as high as 97% and can be used in process design and theoretical analysis. Finally, based on the relationship between stress relaxation and creep, an implicit creep constitutive equation is proposed to describe the stress relaxation behavior. The identified material parameters are input to ABAQUS to simulate the thermal stress relaxation behavior of Ti-6Al-4V It is found that the simulated stress variation accords with the stress relaxation curve, which proves the applicability of the creep constitutive equation to the stress relaxation simulation.