We present an approach to model the mechanical response of multiphase segregated polyurea under large quasistatic uniaxial compression. The approach is based on a two-step procedure. We first conduct all-atom NVE molecular dynamics simulations of the fully-mixed and hard phases of polyurea. We then put forth a model of hard-phase activation based on Taylor, or meanfield, averaging and compute the composite response. The predictions of the present approach, with or without Taylor averaging, show remarkable agreement with data from plate-impact experiments. (C) 2016 Elsevier Ltd. All rights reserved.