Abstract:
The shock sensitivity of RDX (cyclotrimethylenetrinitramine) is dependent
upon factors including crystal size, morphology, internal defects, surface
defects and HMX content. With the arrival of reduced sensitivity RDX (RSRDX)
and the drive towards insensitive munitions (IM), understanding what
influences sensitivity has become a significant topic within energetic materials
research. During the RS-RDX international Round Robin Study (R4) the
parameters which influence sensitivity were investigated, however large
discrepancies were seen between different laboratories so the results were
inconclusive.
The objective of this work is to clarify how crystal properties and the
manufacturing process affect RDX sensitivity. In this study the same RDX lots
as those from the R4 were examined. Optical microscopy showed that internal
defect content varied widely and was affected by the manufacturing process.
A good correlation between sensitivity and defect quantity was seen for RDX
lots produced by the same method. Likewise, microscopic examination also
showed a large range of morphologies which was influenced by method of
production. Scanning electron microscopy also showed that surface defects
were approximately correlated to shock sensitivity, however general surface
roughness agreed better with sensitivity than the number of specific defects
such as cracks and holes. The mechanical properties of the RDX samples were
investigated using nanoindentation. This showed a good correlation between
the quantity of internal defects and modulus of elasticity, hardness and creep.
There was also a good agreement between these parameters and sensitivity.
Rheological analysis of RDX/polyethylene glycol suspensions indicated a good
agreement between the rheological properties of the suspension and crystal
morphology. This method could form a basis for a new testing method for
RDX morphology. Differential scanning calorimetry demonstrated that crystal
size influenced decomposition rate. The melting endotherm onset temperature
and energy was correlated with HMX quantity.
