Phonon spectrum and related thermodynamic properties of microcrack in bcc-Fe

The phonon spectrum and the related thermodynamic properties ofmicrocracks in bcc-Fe are studied with the recursion method by usingthe Finnis--Sinclair (F--S) N-body potential. The initial configuration of the microcracks is establishedfrom an anisotropic linear elastic solution and relaxed to anequilibrium by molecular dynamics method. It is shown that the localvibrational density of states of the atoms near a crack tip isconsiderably different from the bulk phonon spectrum, which isclosely associated with the local stress field around the crack tip;meanwhile, the local vibrational energies of atoms near the cracktip are higher than those of atoms in a perfect crystal. Theseresults imply that the crack tip zone is in a complex stress stateand closely related to the structure evolution of cracks. It is alsofound that the phonon excitation is a kind of local effect inducedby microcracks. In addition, the microcrack system has a highervibrational entropy, which reflects the character of phonon spectrumrelated to the stress field induced by cracks.