Structural analysis aspects of the cookoff modeling problem.

摘要

Although energetic material cookoff is typically regarded as a thermal and chemical problem, the structural response of both the energetic material and the materials encasing the energetic material is an integral part of the process. Both quasistatic and transient structural response regimes occur during a typical cookoff event. The initial heating of the system is a quasistatic event where the timescales of interest are in the range of seconds to hours and the thermal stresses caused by the mismatch of thermal expansion between the energetic material and the confinement are important. However, when the energetic material begins to deflagrate or burn, the structural response enters a dynamic regime in which the timescales of interest are in the range of microseconds to milliseconds and the inertial response of the confinement becomes important. A good example of this is modeling of the deflagration-to-detonation transition (DDT) process. DDT is strongly pressure dependent, and the attainable pressure is dependent on the confinement provided by the structural response of the system. This bidirectional dependence tightly couples the chemical and thermal response of the energetic material and the transient dynamics response of the system. Another example of a tightly-coupled process is the cookoff response of foaming propellants in which extreme temperature causes degradation of binder and oxidizer with associated gas generation and void formation. Gas generation leads to pressure buildup which imposes stresses on the propellant and the confining material which can, in some cases, lead to large deformations and possible breaching of the confinement. In this paper, the structural aspects of cookoff are described followed by a description of the structural analysis tools being developed at Sandia National Laboratories, New Mexico, for these types of problems. The tools being developed include loosely-coupled and tightly-coupled thermal-mechanical analysis codes.