Viscoplastic analysis of plate-impact spallation

J. Eftis, J. A. Nemes, P. W. Randles

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


A model to predict material damage and spall fracture under high strain-rate conditions is applied to plate impact experiments. The model uses the Perzyna viscoplastic constitutive theory, appropriately modified to include a nonlinear isotropic hardening law that allows for saturation of the hardening with increase of strain. The constitutive equation contains a scalar variable for description of the material damage, expressed as the void volume fraction of the polycrystalline solid with microvoids. Incorporation of the damage parameter into the completely phenomenological elasto-viscoplastic constitutive equations permits description of rate-dependent, compressible, inelastic deformation, and ductile fracture. The evolution equation for the parameter describes microvoid nucleation and growth. The model for microvoid growth is based upon a random distribution of microvoids, idealized as spherical holes of arbitrary size. Microvoid coalescence is considered by incorporation of void interaction functions to describe enhanced nucleation and growth rates. A local spall fracture criterion based upon the attainment of a critical microvoid volume is utilized. The constitutive equations are specialized to uniaxial deformation with multiaxial stress, which is appropriate for the planar impact experiments. A finite-difference wave propagation computer code is used to solve the equation of motion. The computed stress wave profiles demonstrate the effect of using a viscoplastic material description. Calculations predicting the rear-surface velocity-time profile and the stress-time profiles of the OFHC copper target are compared with measured profiles. The damage (void volume) distribution across the plate thickness is also calculated and compared with experimental data.

Original languageEnglish (US)
Pages (from-to)15-39
Number of pages25
JournalInternational journal of plasticity
Issue number1-2
StatePublished - 1991

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering


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