Modelling Of Dynamic Tensile Properties And Fracture Of Magnesium Matrix Nanocomposites At Elevated Temperatures

Particulate-reinforced Magnesium-matrix nanocomposites have a wide range of application prospect in military, aerospace, transportation, electronic packaging and other fields due to the highest strength/weight ratio, good mechanical processing performance, relatively high strength, good plasticity and toughness at room temperature, and strong design ability compared to the magnesium alloy materials. The materials for engineering structures usually work under very harsh conditions, such as high temperature and high strain rate. Therefore, it is of great theoretical value and practical significance to study the mechanical properties and fracture damage behavior of magnesium matrix nanocomposites reinforced with nanosized hybrid reinforcements under dynamic loading and high temperature conditions.In this paper, a representative volume element (RVE) model for magnesium matrix hybrid nanocomposites has been established based on the computational micro mechanics method. The dynamic mechanical properties of the heat extruded AZ91 alloy matrix hybrid nanocomposites at high temperature have been analyzed, and compared with the experiment results. The results showed that the hybrid ratio and volume fraction of the nanosized hybrid reinforcements have an important influence on the dynamic mechanical properties of magnesium matrix nanocomposites. The dynamic yield stress and flow stress of the nanocomposites are different with the variation of the hybrid ratio, the mechanical properties of magnesium nanocomposites are increased with the increasement of the volume fraction of the reinforcements, and the dynamic yield and flow stresses of the nanocomposites are increased correspondingly. The nanocomposites have positive strain rate hardening and temperature softening effects at high temperatures and high strain rates. It can also be found that the dynamic mechanical properties of the nanocomposites are increased with the increasement of the volume content of the CNTs by comparing with those of the nanocomposite reinforced by single nanosized reinforcements. In order to analyze the interface debonding between the reinforcements and matrix, and to analyze the dynamic fracture of the nanocomposites at high temperatures, the cohesive elements with finite thickness have been adopted to substitute the interface between the reinforcements and matrix. It can be seen that the damage fracture of the hybrid nanocomposites initiated in the interface debonding, and then cracks appeared and propagated in the matrix until fully fracture. The interfacial strength between the reinforcements and matrix has an important influence on the interface debonding. The greater the interface bonding strength is, the more difficult the interface debonding is. The smaller the interface bonding strength is, the easier the interface debonding occurs. Different volume fraction and volume hybrid radio will have an impact on fracture properties of the composites.