Papers by Author: Shu Sheng Xu

Abstract: The voids in pure Aluminum always exit in the manufacturing process. The Modified Embedded Atom Method (MEAM) potential is employed in the molecular dynamics (MD) simulation at atomic scale to investigate the interaction between voids under the impact loading for pure Aluminum. The distance between the voids distributed along the loading orientation affects the failure mechanism seriously. The results show that there are 3 kinds of mechanisms with the change of the distance between voids: 1) coalescence takes place within a critical distance between voids under extra loading, 2) when the distance between voids reaches a certain value, each void cracks at 4 locations along with the slide direction <110> of face-centered cubic (fcc), respectively, 3) a stress shield zone appears when the ligament between the voids is at the size between the cases mentioned above, which brings out the phenomena that each of the voids cracks only at 2 locations, and no crack appeared at the stress shield zone.

Abstract: Micro-cracks which seriously affect the strength of metal materials always exist in metal or alloys during the manufacturing process. In order to investigate the pre-crack effects on deformation and failure mechanisms for pure aluminum at atomic scale, the plastic deformation processes of pure aluminum with face-centered cubic (fcc) crystal structure around the pre-crack tips at atomic scale were examined by means of molecular dynamics (MD) method. The Modified Embedded Atom Method (MEAM) potential was used to describe the interaction among atoms of pure aluminum. The crack propagation and failure processes for fcc structure were observed near the pre-crack tip zone. The calculation results reveal that the pre-crack blunting occurred at first, then the dislocation emitted at the pre-crack boundary and moved along with the specific direction obviously, eventually, cracks propagated along the crystallographic direction family of <110>. By means of VMD software, the graphic pictures of dislocation movement and crack propagation were obtained under different load conditions. The results and methodology given in this study are very significant for understanding more about plastic deformation and destruction at atomic scale for pure Aluminum with fcc structure.

Abstract: The crack propagation for pure Magnesium at an atomic scale level under external loading was carried out by using a molecular dynamics method. In this study, the Modified Embedded Atom Method (MEAM) was used to characterize the interactions of atoms and the Newtonian equations were solved by Velocity-Verlet algorithm. The crack propagation and failure processes were observed around the crack tip. The calculation results reveal that vacancies were formed near the crack tip during the failure processes for pure Magnesium, and the coalescence between crack tip and vacancies induced the crack growth with the increase in loading.

Abstract: Magnesium alloys are among the best light-weight structural material with a relatively high strength-to-weight ratio end excellent technological properties. Therefore, magnesium attracts special attention of researchers working in automotive and aircraft industry. This work paid the efforts to the structural components made out of magnesium alloy AM60 such as chassis, transmission case in automotive, where the components are subject to cyclic loading after being pre-loaded. In this study, the cyclic stress-strain behaviors were investigated by strain-controlled fatigue testing. In order to investigate the effects of R-ratio on mean stress relaxation, the R-ratio ranged from 0.1 to 0.7 at the strain amplitude of 0.3%. The experimental results indicate that the mean stress relaxation increases with the increasing R-ratio. A constitutive model was proposed to simulate the mean stress relaxation. The calculation results show that the constitutive model developed in this work is capable of reproducing the stress relaxation behaviors of magnesium alloy AM60 under strain control.