A multiscale continuum fragmentation model motivated by lower length scale simulations
Gullet, Philip M.
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A multiscale continuum model for fragmentation in ductile metals was developed, motivated by structure-property relationships obtained from lower length scale and numerical simulations. Fragmentation occurs during high strain rate deformation as the result of widespread internal damage in the form of void or crack nucleation, growth, and coalescence. The connection between internal damage structures and fragmentation was determined through Molecular Dynamics (MD) simulations of high rate deformation in copper, iron, and iron-carbon alloys. The fragmentation metric of interest in this study is the fragment size, which is represented in MD simulations by the fragment length scale, or the solid volume per surface area ratio. Three deformation modes of varying stress triaxialities, plane strain tension, equibiaxial expansion, and isotropic expansion, provide a range of damage growth behavior allowing the fragment length scale to be correlated to damage structures under different conditions. Modified Embedded Atom Method (MEAM) potentials for the materials enable the representation of damage (and newly created free surfaces) under the extreme conditions. Continuum, nonhomogeneous percolation simulations establish a criterion for fragmentation based on internal damage structure. The continuum percolation simulations are motivated by void size and shape information taken from experimental fracture surfaces of an aluminum 7085 alloy. The combination of the percolation based fragmentation criterion and MD motivated fragmentation model yields a framework for the multiscale modeling of fragmentation.