镁基复合材料高温高应变率本构关系及验证

发布时间：2018-04-23 05:20

本文选题：镁基复合材料 + Johnson-Cook本构关系　；参考：《大连理工大学》2016年硕士论文

【摘要】：镁合金因其潜在的物理和力学性能被广泛用于电子、汽车等工业领域。为了改善镁合金的力学性能以满足不同领域对其的需求,越来越多的研究者开始研究纳米增强镁基复合材料的力学性能。但是,这些研究者主要是研究材料在室温以及静态/准静态条件下的力学行为,而这与实际工况是不相符的。因此,研究镁基纳米复合材料在高温动态荷载下的力学性能具有重要的意义。本文采用霍普金森拉杆(Split Hopkinson Tension Bar, SHTB)实验装置测试了镁基纳米复合材料在高温高应变率下的力学性能,得到了一系列的应力应变曲线。在原始实验数据的基础上进行了温度修正,同时在考虑温度和应变率之间的耦合作用的条件下对标准Johnson-Cook (J-C)本构模型进行了两次修正(Modified和Proposed模型),并采用温度修正后的实验数据对标准J-C和修正J-C本构模型都进行了参数拟合。将拟合结果与实验结果对比发现,修正的J-C本构模型(Proposed模型)可以更好地描述材料在高温高应变率下的力学行为。本文采用Johnson-Cook (J-C)动态破坏本构模型来描述材料在高温高应变率下的失效行为,并根据实验结果拟合出了相关参数。详细推导了VUMAT子程序的应力更新算法,并将修正的J-C本构模型和J-C破坏本构模型编写到VUMAT子程序中。在此基础上,基于SHTB实验装置建立了有限元模型进行了数值模拟分析。结果表明,采用修正本构(Modified Model)模拟得到的结果与实验结果吻合更好,而新提出的本构(Proposed Model)则更适合描述复合材料在高温高应变率下的力学性能。为了验证复合材料的本构关系,本文采用数值模拟的方法进一步研究了镁基纳米复合材料板材在冲击荷载作用下的变形行为。首先,在一定厚度和尺寸下研究了镁复合材料板材在低速反复冲击下的变形行为；其次,在等面密度的基础上研究了镁基复合材料在高速冲击下的变形行为,并将模拟结果与已有文献实验结果对比,结果表明：在平顶冲头作用下,镁基复合材料板材的弹道极限速度值与1100-H12铝合金具有一定可比性。
[Abstract]:Magnesium alloys are widely used in electronic, automotive and other industries because of their potential physical and mechanical properties. In order to improve the mechanical properties of magnesium alloys to meet the needs of different fields, more and more researchers began to study the mechanical properties of nano-reinforced magnesium matrix composites. However, these researchers mainly study the mechanical behavior of the materials at room temperature and under static / quasi-static conditions, which is inconsistent with the actual working conditions. Therefore, it is of great significance to study the mechanical properties of magnesium matrix nanocomposites under high temperature dynamic loading. In this paper, the mechanical properties of magnesium matrix nanocomposites at high temperature and high strain rate have been measured by using the Hopkinson split Hopkinson Tension Bar. a series of stress-strain curves have been obtained. Based on the original experimental data, the temperature correction is carried out. At the same time, the standard Johnson-Cook J-C constitutive model is modified twice under the condition of considering the coupling between temperature and strain rate, and the modified J-C constitutive model and the standard J-C constitutive model are analyzed by using the temperature modified experimental data. Parameter fitting is carried out. It is found that the modified J-C constitutive model / proposed model can better describe the mechanical behavior of the material at high temperature and high strain rate. In this paper, the dynamic failure constitutive model of Johnson-Cook J-C is used to describe the failure behavior of materials at high temperature and high strain rate, and the relevant parameters are fitted according to the experimental results. The stress updating algorithm of VUMAT subroutine is deduced in detail, and the modified J-C constitutive model and J-C failure constitutive model are written into the VUMAT subroutine. On this basis, the finite element model based on SHTB experimental device is established and analyzed numerically. The results show that the modified constitutive model is more suitable to describe the mechanical properties of composites at high temperature and strain rate, while the new constitutive model is more suitable to describe the mechanical properties of the composites at high temperature and high strain rate. In order to verify the constitutive relationship of composite materials, the deformation behavior of magnesium matrix nanocomposite plates under impact loading was further studied by numerical simulation. Firstly, the deformation behavior of magnesium composite plate under low speed and repeated impact is studied at a certain thickness and size; secondly, the deformation behavior of magnesium matrix composite under high speed impact is studied on the basis of iso-plane density. The simulation results are compared with the experimental results. The results show that under the action of flat-top punch, the ballistic limit velocity of magnesium matrix composite plate is comparable to that of 1100-H12 aluminum alloy.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB333

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