Molecular dynamics study on mechanical properties and fracture in amorphous metal

The dynamics of atomic arrangement observed on a microscopic scare in amorp hous iron are analyzed in detail to obtain the mechanical properties and fr acture mechanisms of amorphous metal. First, an amorphous model specimen cr eated by a melting and rapid-quenching process by computer simulation is te sted by molecular dynamics (MD) under uniaxial preloading and subsequent bi axial reloading. This process can directly deal with phenomena at atomic sc ale. 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 yi eld stress. Next, the MD simulations of mode I crack propagations are carri ed out. The J integral, one of the representative mechanical parameters oft en used as a criterion of crack propagation in continuum mechanics, is eval uated. The changes of mechanical properties are concerned with the material damage and the geometrical nonlinearity of a blunted tip, which may be pre dicted quantitatively by using J* integral that is evaluated by choosing th e appropriate integral region.