ALE3D model predictions and materials characterization for the cookoff response of PBXN-109

ALE3D simulations are presented for the thermal explosion of PBXN-109 (RDX, Al, HTPB, DOA) in support of an effort by the U. S. Navy and Department of Energy (DOE) to validate computational models. The U. S. Navy is performing benchmark tests for the slow cookoff of PBXN-1 09 in a sealed tube. Candidate models are being tested using the ALE3D code, which can simulate the coupled thermal, mechanical, and chemical behavior during heating, ignition, and explosion. The strength behavior of the solid constituents is represented by a Steinberg-Guinan model while polynomial and gamma-law expressions are used for the equation of state of the solid and gas species, respectively. A void model is employed to represent the air in gaps. ALE3D model parameters are specified using measurements of thermal and mechanical properties including thermal expansion, heat capacity, shear modulus, and bulk modulus. A standard three-step chemical kinetics model is used during the thermal ramp, and a pressure-dependent bum front model is employed during the rapid expansion. Parameters for the three-step kinetics model are specified using measurements of the One-Dimensional-Time-to-Explosion (ODTX), while measurements for burn rate of pristine and thermally damaged material are employed to determine parameters in the burn front model. Results are given for calculations in which heating, ignition, and explosion are modeled in a single simulation. We compare model results to measurements for the cookoff temperature and tube wall strain.