Ti-6Al-4V绝热剪切形变中热/力学参量的数值模拟及其剪切带内微观组织演化机制的探讨

【作者】 程信林；

【导师】 杨扬；

【作者基本信息】 中南大学 ， 材料加工工程， 2004， 硕士

【摘要】 绝热剪切是金属材料在高应变速率变形条件下常见的一种现象。钛及钛合金由于其优良的性能被广泛应用于航空、航天等重要工业部门，同时钛对绝热剪切敏感，在高应变速率形变条件下易产生所谓的绝热剪切带，而关于绝热剪切带内的微观组织演化规律是人们研究的焦点。我们在所作的前期工作及国内外的研究成果的基础上，应用C语言程序实现了最小二乘法拟合热一粘塑性本构方程中待定参数的求解过程；在此基础上应用DEFORM 2D有限元分析系统对，Ti-6A1-4V绝热剪切过程中的热一力变化历史进行了分析；在数值模拟结果的基础上，进行了再结晶动力学的分析与计算。研究结果表明：应用Johnson-Cook热一粘塑性本构模型能够在较大的温度和应变速率范围内精确地预测Ti-6A1-4V的流变应力；有限元模拟结果揭示了材料在绝热剪切过程中的热一力学场量的分布规律，这些场量的分布规律不但映证了在绝热剪切形变过程中应力、应变的高度局域化，同时也在理论上预测了热塑失稳的发生；再结晶动力学的计算结果表明：在发生绝热剪切过程中，虽然绝热剪切带内的最大绝热湿升大大超过了O．4Tm，但存随后的冷却过程中温度下降地很快，而使其内温度保持存0.4Tm以上的时间很短，还不足以在冷却过程中发生静态再结晶，传统的由扩散控制的动态再结晶机制也不能用来解释其内的微观组织变化。表明在高应变速率变形条件下，扩散不是控制动态再结晶的唯一因素，应用一种基于力学辅助的动态再结晶机制能够较好地解释其内的微观组织变化。而关于这种模犁的定量研究将是我们今后工作的重点。更多还原

【Abstract】 The adiabatic shearing phenomena were often found in metallic materials under high-strain, high-strain-rate deformation.Ti and Ti alloy were applied widely in airline and aerospace industry because of its excellent performance.Ti is also sensitive to adiabatic shearing and easy to form adiabatic shear band (A SB).Now many research focus on the microstructural evolution mechanism in ASB.Based on the early works, the C program language and the least square method were used to obtain the thermal viscoplastic constitutive equation.A mechanical thermal coupled model was created and DEFORM-2D was used to analyze the thermal and mechanical parameters’ changing during the process of adiabatic shearing.With the simulation result, the Ti alloy’s dynamics of recrystallization were calculated and analyzed.The conclusions of this research indicated: The obtained constitutive equation based on Johnson-Cook model can accurately predict the flow stress.FE simulation result discovered the parameters distribution result which not only consisted with the experimental result but also predicted the unsteady point.According to the result of dynamics calculation, the adiabatic temperature rising was higher than 0.4Tm, but the duration time above 0.4Tm is very short and not enough for static recrystallization process.Traditional diffuse-controlled recrystallization mechanism can not account for the microstructural evolution in ASB.This indicated that diffuse is not the only controlled factor for recrystallization under high-strain-rate deformation.A mechanical assistant model can apply to account for the microstructural evolution in ASB, and the quantitative research on this model is the emphases of our future work.更多还原