Abstract
The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during mechanical deformation, but characterizing the microstructure can be challenging. For example, the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient X-ray contrast to obtain three-dimensional data by in situ, absorption contrast imaging. To address this difficulty, we have formulated a series of PBXs using octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals and low-density binder systems. The binders were hydroxyl-terminated polybutadiene (HTPB) or glycidyl azide polymer (GAP) cured with a commercial blend of acrylic monomers/oligomers. The binder density is approximately half of the HMX, allowing for excellent contrast using in situ X-ray computed tomography (CT) imaging. The samples were imaged during unaxial compression using micro-scale CT in an interrupted in situ modality. The rigidity of the binder was observed to significantly influence fracture, crystal-binder delamination, and flow. Additionally, 2D slices from the segmented 3D images were meshed for finite element simulation of the mesoscale response. At low stiffness, the binder and crystal do not delaminate and the crystals move with the material flow; at high stiffness, marked delamination is noted between the crystals and the binder, leading to very different mechanical properties. Initial model results exhibit qualitatively similar delamination.
Highlights
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a powerful high explosive that is routinely used in a variety of plastic bonded explosive (PBX) formulations such as plastic bonded explosives (PBXs) 9501.Many HMX-based PBXs are highly loaded (10% or less binder) and exhibit bimodal or trimodal particle size distribution in the size range of single to hundreds of micrometers
The full details of such mesoscale modeling approaches are beyond the scope of this paper, but below we provide a brief overview of the treatments applied here
It is likely that other PBX materials fall into this spectrum of possible responses, enabling us to conduct simulations and validation experiments without needing to perform full microstructural characterization of every single sample
Summary
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a powerful high explosive that is routinely used in a variety of plastic bonded explosive (PBX) formulations such as PBX 9501. Many HMX-based PBXs are highly loaded (10% or less binder) and exhibit bimodal or trimodal particle size distribution in the size range of single to hundreds of micrometers. The microstructure of PBX materials is known to directly influence fracture behavior [1,2], mechanical properties [3,4], and thermal properties [5,6]. Microstructural behavior is believed to strongly affect the initiation. Microstructure-based effects such as binder thermal expansion and ventilation pathways through the material have been shown to influence time-to-ignition in cook-off of PBX 9501 [9]
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