Tension and compression effect on mechanical properties of Fe and B2

The elastic constants, ideal strength, band structure and electronic density state of Fe and B2 under tension and compression were studied by using the first principle. The structural parameters calculated at 0 pressure are consistent with the experimental results. The dependence of elastic constant and stress can be obtained by using static finite strain technique. The ideal tensile and compressive strength of Fe and B2 were studied by calculating the stress-strain relationship. At last, the micro mechanism which affects the stability of the structure was analyzed by using the results of electronic structure calculation. The results show that the compressive strength of Fe and B2 structure is higher than the tensile strength. When the stress of cell structure exceeds a limit, it will be destroyed, resulting in the sudden decrease of Poisson's ratio, B and G, the asymmetry of energy band structure and the decrease of electron density of state energy. (paper)