Molecular dynamics study on mechanical properties and fracture in amorphous metal

The dynamics of atomic arrangement observed on a microscopic scale in amorphous iron are analyzed in detail to obtain the mechanical properties and fracture mechanisms of amorphous metal. First, an amorphous model specimen created by a melting and rapid-quenching process by computer simulation is tested by molecular dynamics (MD) under uniaxial preloading and subsequent biaxial reloading. This process can directly deal with phenomena at atomic scale. The results of the simulation show that the initial properties of the model are recovered even if it is subjected to strains closely approaching the maximum loading point. However, further excess loading causes a change of atomic structure and a remarkable decrease of its elastic modulus and yield stress. Next, the MD simulations of mode I crack propagations are carried out. The J integral, one of the representative mechanical parameters often used as a criterion of crack propagation in continuum mechanics, is evaluated. The changes of mechanical properties are concerned with the material damage and the geometrical nonlinearity of a blunted tip, which may be predicted quantitatively by using J * integral that is evaluated by choosing the appropriate integral region.