Properties of binders in polymer bonded explosives may lead to better designs
Properties of binders in polymer bonded explosives may lead to better designs lead image
To better understand the mechanical responses of polymer bonded explosives and to improve their efficiency and safety, scientists explore the properties and characteristics of the binder. This is not without its challenges. Soft solid materials, such as binders in explosives, can be hard to model due to their softness.
Iqbal et al. collect rheological information on the properties of a nitrocellulose-based visco-hyperelastic binder in polymer bonded explosives. To characterize the binder in relation to its shear and tensile responses, they use constant shear strain rate, shear stress relaxation and monotonic tensile tests.
“In PBX, the binder volume fraction is typically 5% - 25%. However, despite having a low volume fraction, because of the large difference between the binder and filler stiffnesses, the overall PBX material properties depend highly on the binder. The strength of the binder-explosive crystal interface is also very important,” said author Maria Charalambides.
The authors developed a constitutive model based on visco-hyperelasticy using the new data. This model, which has commercial uses, was validated through finite element simulations.
“To our knowledge, no one has studied the effect of normal force rising during continuous shear testing of soft solids on the recorded data. There is more literature on rheological testing of complex fluids, less so on soft solids. In our work, we have highlighted this effect and we propose methods for how to determine the valid range for the recorded data,” said Charalambides.
In the future, the authors suggest this model be implemented inside micromechanical simulations of explosive composite materials, which have nitro-cellulose-based material as a matrix. The authors hope to expand the existing model to include damage or fracture.
Source: “Mechanical characterization of the nitrocellulose-based visco-hyperelastic binder in polymer bonded explosives,” by M. Iqbal, J. Y. S. Li-Mayer, D. Lewis, S. Connors, and M. N. Charalambides, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5135093 .
