Dislocation - Assisted Initiation of Energetic Materials

 

Ronald W. ARMSTRONG

Center for Energetic Concepts Development,
University of Maryland, College Park, MD 20742, U.S.A.

Abstract:The role of dislocations in assisting initiation of (explosive) chemical
decomposition of energetic materials has connection with the known influences for
crystals and polycrystals of dislocations facilitating permanent deformations and
phase transformations. X-ray topographic observation of relatively few dislocations
in solution-grown crystals relates to the influence of large Burgers (displacement)
vectors that are characteristic of molecular crystal bonding. Both model evaluations
of the load dependence of cracking at hardness indentations and the derived hardness
stress-strain behaviors show that dislocation movement is difficult whether in the
indentation strain fields or at the tips of indentation-induced cracks. Thus, energetic
crystals are elastically compliant, plastically hard, and relatively brittle [1].
Nevertheless, cracking is shown to be facilitated by the shear stress driven, normally
limited, dislocation flow that, on molecular dynamics and dislocation pile-up model
bases, is shown to be especially prone to producing localized hot spot heating for
explosive initiations. Such model consideration is in agreement with greater dropweight
heights being required to initiate smaller crystals. The crystal size effect carries over
to more difficult combustion occurring for compaction of smaller crystals. The total
results relate to dual advantages of greater strength and reduced mechanical sensitivity
accruing for the development of nanocrystal formulations. In consequence, also,
several levels of dislocation-assisted modeling are described for initiation mechanisms
under shock wave loading conditions.

Keywords:dislocations, initiation, energetic crystals, x-ray topography, hardness,
cracking, drop-weight impact, combustion, shock wave loading, crystal growth,
plasticity, RDX, PETN, HMX, hot spots, sensitivity, crystal lattice modeling