Insensitive Munitions & Energetic Materials Technology Symposium
April 23 - 26, 2018
Portland, OR
Thermal modeling of fast cook-offs
Markus Graswald and Raphael Gutser
TDW Gesellschaft f
¨
ur verteidigungstechnische Wirksysteme mbH
Hagenauer Forst 27, 86529 Schrobenhausen, Germany
Abstract
Being fully compliant to Insensitive Munitions (IM) requirements is of utmost importance for today’s
and future munitions. The IM approach as defined in AOP-39 is typically performed by using insensi-
tive plastic-bonded high explosives (PBX) and assessing IM states and mitigation technologies on war-
head system, munition, and, if necessary, munition packing level. Among other IM hazards listed in
STANAG 4439, thermal stimuli through fast cook-off heating are usually of particular interest for large
warheads and bombs, since they may strongly drive the warhead system design and shall be evaluated
at the earliest opportunity.
A simplified approach applies a transient FE model in ANSYS with a typical flame temperature
profile that allows predicting temperatures and times during a fast cook-off. Such investigations are used
to evaluate potential areas of hot spot forming and critical components that may indicate the need for
specific mitigation measures.
In a new approach, a reaction kinetic model originally developed for modeling self-heating of explosive
charges at slow cook-offs and implemented into COMSOL is adapted for fast cook-off simulations. Dif-
ferential scanning calorimetry (DSC) tests of small explosive samples at fast heating rates provide input
data required. Parameters for self-heating of the explosive charge are derived with AKTS-Thermokinetics
software fitted to such experimentally determined heating curves. This data is eventually implemented
into COMSOL simulating fast cook-off behavior of full-scale warheads. This results in an accurate pre-
diction of spatial temperature profiles as well as reaction times and temperatures. In addition, mitigation
potential through intumescent coatings on the casing are assessed that provide an effective insulation
layer and lead to significant reaction time delays.
1 Introduction
Insensitive Munitions (IM) requirements are very relevant for today’s and future munitions. Among all
IM hazards listed in STANAG 4439 [1], thermal stimuli such as slow and fast cook-off (SCO / FCO)
heating are particularly interesting, since they may have a significant impact on the design of warheads
using large and / or strongly confined high explosive (HE) charges. A number of fast cook-off studies
investigate the heat transfer of a fire on test vessels through both experimental and modeling means,
e.g. [2, 3, 4]. The influence of wind on flame temperatures in a large-scale experiment of a truck-sized
nuclear waste transport package are reported in [5]. Recent thermal analysis and modeling efforts apply
For further information: markus.graswald@mbda-systems.de, +49 (8252) 99-7264.
