An anisotropic deformation analysis of orthotropic materials subjected to high velocity impacts

A finite strain constitutive model to predict a complex elastoplastic deformation behaviour involves very high pressures and shockwaves in orthotropic materials is developed in this work. The important feature of the proposed hyperelastic-plastic constitutive model is a Mandel stress tensor combined with the new generalised orthotropic pressure. The formulation is developed in the isoclinic configuration and allows for a unique treatment for elastic and plastic orthotropy. The elastic orthotropy is taken into account through a stress tensor decomposition combined with the new pressure. A yield surface of Hill’s yield criterion aligned uniquely within the principal stress space is adopted to characterise plastic orthotropy by means of the evolving structural tensors. An isotropic hardening is adopted to define the evolution of plastic orthotropy. The formulation is further combined with a shock equation of state (EOS) and Grady spall failure model to predict shockwave propagation and spall failure in the materials, respectively. The proposed constitutive model is implemented as a new material model in the Lawrence Livermore National Laboratory (LLNL)-DYNA3D code of UTHM’s version. The ability of the newly constitutive model to describe finite strain deformation and shock propagation in orthotropic materials is first investigated against plate impact data of aluminium alloy in the longitudinal and transverse directions before a comparison against plate impact test data of carbon fibre reinforced epoxy composites along the through-thickness direction is finally conducted. A good agreement is obtained in each test