Papers by Author: Ya Fang Guo

Abstract: The mechanisms of low-temperature deformation around a crack tip in a hexagonally closed-packed (hcp) magnesium single crystal have been studied by molecular dynamics simulations. In our simulation a {1010} < 12 10 > model I (opening model) crack is selected. The results indicate that slip on the basal plane is activated due to the shear stress at the crack tip. Thus shear banding caused by a successive slip of the basal planes is the main deformation way for this type of crack.

Abstract: Molecular dynamics (MD) simulations with an EAM potential are carried out to study the strain rate effects on the tensile deformation of single-crystal copper films. The stress, the atomic energy, as well as the atomic configurations of the systems are presented to explore the strain rate effects on copper films. It is found that yield stress increases with loading rate. Meanwhile, deformation mechanisms with different strain rates are analyzed in the present work. At lower strain rate, slips along {111} planes are primarily responsible for the plastic deformation in nano-Cu films. As strain rate increased, the motion of dislocations becomes easier, a transition of the deformation mechanism from sequential propagation of slips along well-defined slip planes to complex cross-slip.

Abstract: A quantitative life prediction method has been proposed to evaluate fatigue life during morphological evolution of precipitates in Ni-based superalloys. The method is essentially based on Eshelby’s equivalent inclusion theory and Mori-Tanaka’s mean field method. The shape stability and life prediction are discussed when the external stress and matrix plastic strain are applied. The calculated results show that the fatigue life is closely related with microstructures evolution of precipitates. The magnitude and sign of the external stress and matrix plastic strain have an important effect on fatigue life of Ni-based superalloys during the morphological evolution of precipitates.

Abstract: In this paper, the continuous in-situ observations of the fatigue crack growth in U71Mn and U75V rail steel are made by using the scanning electronic microscope (SEM). The microstructure patterns of cracks under the mode I fatigue loads and quasi-static loads are presented. The results indicate that the short fatigue crack growth in rail steel is a quasi-cleavage fracture. The ductility and the performance of fatigue resistance of U71Mn rail steel are better than those of U75V rail steel.