基于M-K模型的TA15钛合金高温成形极限

为了探究TA15钛合金高温环境下的成形极限，明确本构方程中参数对成形极限的影响规律，建立了考虑高温软化效应TA15钛合金高温环境下的本构关系，利用高温成形极限试验平台及M-K失稳理论对TA15钛合金板高温环境下的成形极限分别进行了试验测试及理论预测。理论预测结果表明当温度从800℃提升至880℃时，平面应变状态下的极限主应变由0.18提升至0.33。基于M-K失稳理论和建立的高温本构模型，分析了本构方程中的参数对成形极限的影响规律，结果表明提高加工硬化指数、速率敏感因子及减小软化因子，均可以提升应变强化率的大小，进一步延缓沟槽内应变状态趋于平面应变状态，从而提升理论成形极限曲线在应变空间中的位置。此外，理论计算结果表明速率敏感因子对成形极限曲线的左侧影响程度要大于其对右侧部分的影响，该现象主要归因于速率敏感因子对不同应变大小下的应变强化率的影响不同。 

Hot forming limit of TA15 titanium alloy based on M-K model

In order to investigate the forming limit of TA15 titanium alloy at high temperature and clarify the influence of parameters in the constitutive equation on the forming limit, the constitutive relationship of TA15 titanium alloy in high temperature environment was established considering the high temperature softening phenomenon, and meanwhile, the forming limit of TA15 titanium alloy plate at high temperature was obtained by high temperature forming limit test platform and theoretical predicted through applying the M-K instability theory, respectively. The theoretical results indicate that the major strain under the plane strain state increases from 0.18 to 0.33 when the temperature increases from 800℃ to 880℃. Based on the M-K instability theory and the established high temperature constitutive model, the influence of the parameters in the constitutive equation on the forming limit is analyzed. The results show that, increasing the values of hardening index and the rate sensitivity factor, and decreasing the value of the softening factor can increase the strain hardening rate, and consequently the strain state in the groove region is delayed approaching the plane strain state. Therefore the position of the forming limit curve in strain space is improved. At the same time, the theoretical calculation results show that the influence of the strain rate sensitivity factor on the left side of the forming limit curve is greater than that on the right side, and it is attributed to the fact that the effect of the strain rate sensitivity factor on the strain hardening rate under different strain size is different.