Computational Aspects of the ARA Three Invariant Constitutive Model

摘要

The three invariant elastoplastic constitutive model has been implemented for use in finite difference blast and shock calculations. The model employs two yield surfaces with an independent plastic potential to control shear induced dilatancy. The model is conceptually similar to Lade's cohesionless soil model. Several improvements in the original ARA model have been incorporated during the course of implementation including tensile strength, expansive strain tracking during tensile failure, optional elimination of work softening, and a high pressure-temperature equation of state. Strain subcycling has been used to prevent violation of the consistency condition. Results are given for planar, spherical, and cylindrical one dimensional wave propagation, and are compared with results using several other currently available constitutive models. Two dimensional DIHEST calculation results are also shown. These calculations employed a newly developed interface between the Soil Element Model (SEM) subroutines and STEALTH 2D. This approach allows the SEM to act as a central bank of material models for potentially any number of continuum codes. Overall, the new constitutive model is physically realistic, somewhat expensive to run, and promising for future application. Steps which remain to make the model more useful in practice include parameter sensitivity studies to help dynamic insitu behavior prediction, improved algorithms for eliminating numerical errors, a rezoning procedure, and more two dimensional calculational experience.