Dynamic overshoot in -iron by atomistic simulations

We present large-scale molecular dynamic simulations of microcrack growth in -iron based on an N-body potential model which gives a good description of defect energetics, anisotropic elasticity and phonon frequency spectra. We demonstrate dynamic overshoot of a pre-existing microcrack under impact loading. We show that the basic behaviour of the simulations is in agreement with the predictions of continuum models. Dynamic phenomena, such as scattering of stress waves at crack faces, acoustic emission (due to bond breakage) and reflections of the stress waves from sample borders, are studied here in detail. The results on microcrack growth, unimpeded by the wave reflections from external sample borders, indicate that under fast loading or at high crack velocities, i.e. under high strain rates, transient twin formation is possible from the crack tip with later detwinning at free crack faces as the crack advances: a twinning equivalent to virtual Knott dislocations.