L-217 Ageing Of Munition Materials
October 2019Wade G. Babcock, Kevin M. Jaansalu
The ageing of materials in munitions as reported in the open literature is reviewed within the framework of materials engineering. The focus is on polymeric materials and molecular solids encountered in energetic materials. Ageing phenomena addressed include thermal degradation, oxidation, and electromagnetic radiation and their effects on the structure and bonding within a material. Nitrocellulose, RDX, and HMX are examined in detail. Gains in understanding of the relative roles of chain scission and oxidation are reviewed and put into context. Chain scission is part of the normal ageing process and associated with reaction mechanisms determined by the chemistry within the polymer. A better understanding of the relative rates oxygen diffusion versus oxidation reactions in polymeric materials, and an ability to model these phenomena, represent a great step forward. For composite materials, used in solid rocket motors, understanding of ageing starts with the pure binder material and then the different effects of the reinforcement can be taken into account. This includes processing defects, changes in diffusion behaviour, and compatibility and their influence on chemical degradation.