Study of the theoretical tensile strength of Fe by a first-principles computational tensile test

This paper employs a first-principles total-energy method to investigate the theoretical tensile strengths of bcc and fcc Fe systemically. It indicates that the theoretical tensile strengths are shown to be 12.4, 32.7, 27.5 GPa for bcc Fe, and 48.1, 34.6, 51.2 GPa for fcc Fe in the [001], [110] and [111] directions, respectively. For bcc Fe, the [001] direction is shown to be the weakest direction due to the occurrence of a phase transition from ferromagnetic bcc Fe to high spin ferromagnetic fcc Fe. For fcc Fe, the [110] direction is the weakest direction due to the formation of an instable saddle-point ＇bct structure＇ in the tensile process. Furthermore, it demonstrates that a magnetic instability will occur under a tensile strain of 14%, characterized by the transition of ferromagnetic bcc Fe to paramagnetic fcc Fe. The results provide a good reference to understand the intrinsic mechanical properties of Fe as a potential structural material in the nuclear fusion Tokamak.

Ab initio investigation of the mechanical properties of copper

Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have systematically investigated the theoretical mechanical properties of copper （Cu）. The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the （110） planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the （111） planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young＇s modulus Ep, and Poisson＇s ratio ~.

Ideal tensile strength of chromium by first-principles method

The ideal tensile strengths of Cr along [001],[110] and [111] directions were calculated based on the first-principles method.The results show that the ideal tensile strengths are 30.83,37.2 and 35.49 GPa for antiferromagnetic Cr,while they are 33.09,47.15 and38.11 GPa for non-magnetic Cr along [001],[110] and[111] directions,respectively.It is obvious that [001] is the weakest direction.When the loading is applied on the direction [001],the ideal tensile strength is reached before the shear instability for both the anti-ferromagnetic and non-magnetic Cr;thus,Cr fails by cleavage and it is deemed to be intrinsically brittle.Meanwhile,for the antiferromagnetic Cr,the correlation between the magnetic moment and volume was analyzed,and the result shows that the magnetic moment increases with the increase in volume and eventually disappears with the increase in strain.In addition,the density of states in the process of loading was also discussed.