Atomistic Study on Crack Propagation in Amorphous Metal

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In order to study the crack propagation properties in amorphous material which has no long-range ordered structure, molecular dynamics simulation has been carried out. A model amorphous has been produced by a simulation of heating-rapid quenching process for an atomic aggregation under interaction prescribed by FS-potential. An edge crack is introduced in two model amorphous, which are (A) a thick plate model with periodic structure in the thickness direction (-one million atoms) and (B) a thin plate modes with stress free surfaces (-two million atoms), and increasing edge loading to bring about the mode I type opening is applied. Main results obtained are :(1) Two types of process zone are formed in the crack front zone, i.e. localized band-like shear deformation and localized density decrease or thinning caused by hydrostatic tensile stress. The former is remarkable in model A and the latter is in model B.(2) In model A, extraordinarily blunting of the crack tip proceeds due to localized shear deformation extending toward the direction of 45°from the tensile axis. The temperature in the process zone rises over 800K, but recrysterization does not occur.(3) In model B, the crack advances remarkably in the following cyclic process : the crack-tip becomes sharp once and voids nucleate and grow in the front region promoting the high hydrostatic tensile stress, and then coalescence of the crack and void occurs and the tip moves forward suddenly. The process zone is limited to a small area.