The Constitutive Behavior And Deformation Mechanism Of Magnesium Matrix Hybrid Nanocomposites Under High Temperature And Dynamic Tensile

Magnesium alloy matrix nanocomposites have been widely used in industry due to their excellent mechanical properties. Researches have been conducted on their static and quasi-static mechanical properties at room temperature, but few investigations are focused on their dynamic mechanical properties. So it is very important to study their dynamic mechanical properties under high stain rate and elevated temperature. This is important for the potential application of magnesium alloy matrix nanocomposites in industry.In this paper, the AZ91magnesium alloy nanocomposites are processed with high-energy ultrasonic stirring. The carbon nanotubes(CNTs) and SiC nanoparticles are used as the reinforcements and the total mass fraction is lwt.%but hybrid ratio of CNTs and SiC nanoparticles is different. The Split Hopkinson Tensile Bar is used to test mechanical properties of the nanocomposites under high strain rate and high temperature. The experimental research focuses on the following aspects:(1) the effects of different hybrid ratio of reinforcements on the effects of the dynamic tensile mechanical properties and constitutive behavior of magnesium alloy matrix nanocomposites under high strain rate and elevated temperature,(2) the effects of different temperature on the dynamic tensile mechanical properties and mechanism of fracture and damage,(3) the effects of different strain rate on the dynamic tensile mechanical properties under high strain rate and elevated temperature. The results show that:(1) the different dynamic mechanical performances of the composites under high temperature are related to different hybrid ratio,(2) the dynamic mechanical properties of the composites are effected by the variations of temperature, the flow stress and tensile strength of the composites decrease as the temperature increasing,(3) the flow stress and tensile strength of the composites increase with the increment of strain rate, indicating the positive strain rate sensitivity of composites,(4) the composites have strain rate hardening and softening effect under dynamic tensile loads and high temperature.The Johnson-Cook constitutive model and Johnson-Cook dynamic failure model are used to describe the tensile stress-strain relationship under high strain rate and high temperature in this paper. The material constants of constitutive and failure model are obtained from the quasi-static and dynamic experiments. The J-C constitutive model and J-C dynamic failure model are employed in3D finite element software ABAQUS to simulate the SHTB experiments at elevated temperature, the numerical simulation results are agreement well with experiment results.Based on the computational micromechanics theory, a three-dimensional representative volume element (RVE) model is built for the composites with reinforcement random distribution and the dynamic tensile simulation is conducted under high temperatures. According to the simulation results, the effect of material meso-scale characteristics (such as content and hybrid ratio of reinforcement) on the dynamic mechanical performance of the composites have been discussed. The results show that:(1) the flow stress and tensile strength of this composites would change with the changes of the content and hybrid ratio of reinforcements,(2) the mechanical performance of the composites would change with the changes of the loading directions and the anisotropic of composites is confirmed,(3) the tendency of the mechanical properties and constitutive behavior of the composites from simulated results is basically same with the experiment results.The research of this paper was supported by the National Nature Science Fundation of China.(No.11272072)...