Molecular Dynamic Simulation On Mechanical Behavior Of Nano-bicrystal Copper Under Uniaxial Tension

Metallic bicrystal is an intermediate form between single crystal and polycrystal. The study of bicrystal serves as a guide to understand and analyze some certain mechanical behaviors of polycrystalline materials. Three-dimensional molecular dynamics (MD) simulations are employed to investigate the elastic mechanical properties of nano-bicrystal Cu under uniaxial tension. In addition, the effects of strain rate, crystallographic orientation and voids, which act on elastic modulus and yield stress, are simulated and studied in detail.The results indicate that the loading strain rate has a strong impact on elastic modulus and yield stress, and they show linear increasing trend with the increase of strain rate. The strain rate effect, acting upon elastic mechanical properties during the process of extension, shows different changing laws in different strain rate regions. At lower strain rate, elastic modulus has no dependence on the loading rate, however, at higher strain rate, it shows clear dependent attribute upon strain rate. Accordingly, there exists a strain rate threshold, which controls the range of these two strain rate regions during the process of tension. Further study shows that the strain rate threshold decreases with the increase of sample size.The effect that elastic modulus response to crystallographic orientation mostly focuses on the following aspects, firstly, it is found that the response curves of elastic modulus and inclination angle is almost symmetric to 900, besides, the angles could be separated into three parts according to the different response trend and one important turning angle is observed in every part. Secondly, elastic modulus decreases and its oscillation attribute become more obvious with the rise of temperature and with the reducing of sample size.Additionally, the effect of voids with different forms on elastic mechanical behavior of bicrystal is also studied and analyzed thoroughly. It is found that the existence of voids weakens the material strength and rigidity seriously. As for the bicrystal copper sample with two symmetric voids with regard to interface, elastic modulus and yield strength shows increasing trend with the elongation of distance between the two voids. Besides, the size of void also plays a significant role during the tension process, and it is found that elastic modulus and yield strength reduce rapidly with the increasing of void radius. On the other hand, as for the sample with voids distributed on the interface, elastic modulus shows different response rule with different void shapes. Size of void makes considerable influence on mechanical properties that elastic modulus and yield stress decrease linearly with the increase of void radius. Finally, the amount effect of voids is studied through make the total volume of the voids hold on a constant and change the number of voids. It is found that elastic modulus and yield strength diminishing with the increase of voids number.