Improvement and fitting of Grüneisen coefficients based on the Finite Strain state equation

Abstract

Accurate simulation of shock initiation in heterogeneous solid explosives relies on the unreacted equation of state (EOS) and reaction rate model. To overcome limitations of existing models for varying densities and complex loading, this study improves the unreacted EOS for a TATB-based polymer-bonded explosive (PBX-1) using Finite Strain theory. The Snowplow model is incorporated to correct the Hugoniot offset caused by density variations, better reflecting the physical state during shock compression. Drawing on Jeanloz and Lambourn’s theories, an improved empirical Grüneisen coefficient formula is developed to more precisely describe the thermodynamic response under non-ideal conditions. Multi-parameter automatic optimization yields parameters for PBX-1 that significantly improve consistency with experimental data. The improved EOS and Grüneisen formula are coupled with the CREST reaction rate model via secondary development and embedded into LS-DYNA. Numerical simulations of square-wave shock initiation experiments on PBX-1 accurately reproduce particle velocity–time histories and outperform the traditional parameter model. These findings verify the effectiveness and reliability of the proposed method in characterizing the shock initiation behavior of TATB-based explosives.