In Situ Imaging during Compression of Plastic Bonded Explosives for Damage Modeling

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.

Investigating deformation and mesoscale void creation in HMX based composites using tomography based grain scale FEM

“…Crystals were paired based on similarly sized flat and parallel faces. The HTPB binder was prepared identically to the low stiffness HTPB binder described in detail in Manner et al [2]. The binder was spread onto the matched face of one crystal while the opposing crystal was placed on top.…”

“…It is known that mesoscale defects such as pores, cracks, and interfacial debonding can alter the mechanical integrity of the composite when subjected to low rate thermo-mechanical loads [1,2]. These defects contribute to heterogeneity in generation of hot spots under dynamic events [3,4].…”

Computational Design of Three-Dimensional Multi-Constituent Material Microstructure Sets with Prescribed Statistical Constituent and Geometric Attributes

“…The first is serial sectioning, a destructive characterization tool that involves cropping, polishing, mounting, and optical microscopy [4][5][6][7]. The second is non-destructive X-ray computerized tomography (CT) [8][9][10][11][12][13][14]. Both methods can be costly, time intensive, and limited in resolution.…”

Characterization of Interfacial Micro‐Structures of Explosive‐Binder Composites by Gas Permeation

“…Besides intrinsic interfacial interactions, the surface structures of the explosive component, e. g. the roughness, also plays an important role in determining the interfacial structures formed within PBXs, as does material processing techniques [6]. These interfacial structures have been studied in multiple scales, from nanometre to centimetre, by utilizing several characterization techniques [5,[14][15][16][17]. Positron annihilation lifetime spectroscopy (PALS), neutron scattering, x-ray computed tomography, and microscopy, have all been employed, though the sensitive nature of explosives and the thin, i. e. nanoscale, nature of the interface means thorough characterization remains challenging.…”