A Constitutive Model For Predicting Dynamic Behavior Of Magnesium Matrix Composites At Elevated Temperatures And Its Validation

Magnesium alloy is widely used in the electronic, auto and other industries due to its potential physical and mechanical properties. In order to improve the mechanical properties of magnesium alloy so as to meet the demand for the different fields, more and more researchers have begun to study the mechanical properties of magnesium matrix composites reinforced by nanosized particles and fibers. However, these investigations are mainly focused on the mechanical behavior at room temperature or static/quasi-static loading, while this is not consistent with the case under the actual working conditions. Therefore, it is of important significance to study mechanical properties of magnesium matrix nanocomposites under the dynamic loading and high temperature conditions.In this paper, a series of experiments are carried out using Split Hopkinson Tension Bar (SHTB) setup with a heating device to determine the mechanical properties of magnesium matrix nanocomposites at high temperatures and high strain rates, and the corresponding stress-strain curves are then obtained. On the basis of original experimental data the temperature correction is accomplished. Based on the standard Johnson-Cook (J-C) constitutive relation, two modified constitutive models such as Modified and Proposed model are developed by considering the coupling effect between temperature and strain rate, and the parameters of these two models are derived from the experimental data after temperature correction. The prediction results of two models are then compared with the experimental results and it is found that the modified J-C constitutive model (Proposed model) can describe the mechanical behavior of the composites at high temperatures and high strain rates much better.The J-C fracture constitutive model is adopted to describe the failure behavior of the composites under high temperature and high strain rate loading, and the relevant parameters are determined according to the experiment results. The revised Johnson-Cook plasticity and fracture models are both implemented in a user-defined subroutine VUMAT of ABAQUS code, and the numerical simulation of the SHTB test for the AZ91D magnesium based nanocomposites at elevated temperatures and different strain rates is carried out using the commercial software ABAQUS 6.9-2/Explicit. Simulation results show that a better agreement with experimental results is obtained using the Modified constitutive model, and that the Proposed constitutive model is more suitable for describing the mechanical properties of the nanocomposites at higher temperatures and higher strain rates.To further verify parameters of the composite constitutive law, numerical simulation is carried out to investigate the deformation behavior of the magnesium matrix nanocomposite plate under impact loading. Firstly, the deformation behavior of the magnesium composite plate with certain thickness and size is studied under low speed and repeated impact loading conditions; Secondly, the deformation behaviour of the magnesium composite plate under high speed impact is studied on the basis of equal areal density, and the simulation results are then compared with the experimental data reported in other's literature. It can be found that the ballistic velocity of the magnesium composite plate is comparable to that of 1100-H12 aluminium alloy under blunt nosed projectile.