A Constitutive Formulation for Anisotropic Materials Suitable for Wave Propagation Computer Programs

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Abstract
The constitutive relationships for an anisotropic material are established for shock wave propagation computer programs, commonly referred to as hydrocodes. In this paper, stresses are formulated in terms of strains for two specific two-dimensional cases: orthotropic behavior in plane strain problems; and transversely isotropic behavior in axisymmetric problems. Additionally, the procedure for separating material nonlinear compressibility effects (equation of state) from strength effects is formulated which per mits the consistent calculation of stresses in the elastic regime, and allows the mean stress and pressure to be defined in accordance with their scalar interpretation. Further, this pro cedure permits the computation of inelastic response by scaling of deviatoric stresses, so the equivalent stress resides on a yield or failure surface, without changing the pressure. In conjunction with this constitutive development, a parallel experimental program was designed and conducted to explosively load fiberglass/epoxy panels in plane strain. This loading induced different levels of damage in the panels such as matrix splitting and delamination between plies. Numerical simulations, using the composite material model, were performed to understand the sequence of the observed failure.

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