Molecular Simulation On Tensile Properties Of Titanium And Aluminum Laminate

This paper mainly studies the tensile property of Titanium and Aluminum laminates. By using molecular dynamics simulation methods, I have analyzed the propagation of dislocations in individual Titanium and Aluminum materials as well as their laminates during uniaxial stretching process. I have also studied the influences on dislocations in Titanium when it is laminated with Aluminum, and whether the size of grains in Aluminum has any effect.To do that, I firstly built a polycrystalline Titanium model with 9 grains, as well as a polycrystalline Aluminum model with 4 grains and 9 grains each. Using the Voronoi theory, I divided the simulation box into several parts, and then I projected a initially built monocrystalline of enough size onto these different parts according to some certain rotation angle. In this way, I built the whole polycrystalline models. The grains in these models are columnar shaped, and their close-packed direction is parallel to the rolling surface. Besides, none of these grains can extend all the way through the x or y direction. Simulate a uniaxial stretching with these models, the outcome stress-strain curves showed a good view of the plastic deformation stage. Furthermore, the curves of the 4-grain Aluminum and 9-grain Aluminum were substantially similar, indicating the models’ rationality.In order to properly analyze the propagation of dislocations within Titanium and Aluminum during loading process, this paper adopts a parametric approach. By calculating in each step the distance between the position where each atom presently is and where it should be if no defects occurred, I got a parameter g. And by analyzing the curves of the g parameter, I can figure out the propagation stage of dislocatiions inside the structure. For a monocrystalline, only one g is needed; while for polycrystalline, each grain has its own g. I firstly used this method to analyze a monocrystalline Aluminum structure with two different boundary conditions under tension, and I found that in both cases g remained close to zero when it’s in elasticity stage, and then when the stress-strain curve reached the highest point, g experienced a sudden jump, indicating a great amount of dislocations has emerged, causing the whole structure to fail.I also used the g parameter method to study the 4-grain and 9-grain Aluminum separately. Both conditions showed that till the strain reached 15%, g remained a steady up-growing trend, and no substantial jump was found, which mean t although the Aluminum had come to a plastic deformation stage, only some few dislocations had occurred, and that the structure could still hold more loading. Applying g method to 9-grain Titanium, I found the g curve rose steeply, and all grains failed when the strain reached 7%, indicating a far worse plasticity property for Titanium than Aluminum. Using the g parameter to analyze the same 9-grain Titanium when it is laminated with the 4-grain Aluminum. Compared with the previous one, g curve had become smoothened dramatically, postponing the failure strain up to 11.3%, which indicated that the Aluminum layer can significantly improve the tensile property of the Titanium layer. Using the g parameter to analyze the same 9-grain Titanium again, this time laminated with the 9-grain Aluminum. The results showed that the tensile property of Titanium layer had improved further, with the failure strain reaching 13.4%, indicating that Aluminum of finer grains can enhance plasticity of Titanium more.