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The current work aims to explore the effective piezoresistive response of polymer bonded explosive (PBX) materials where the polymer medium is reinforced with carbon nanotubes (CNTs). The effective piezoresistive response of these nanocomposite bound polymer explosives (NCBX) is evaluated using micromechanics based 2-scale hierarchical model connecting the CNT-polymer nanocomposite scale (nanoscale) to the explosive grain structure scale (microscale). The binding nanocomposite medium is modeled as electromechanical cohesive zones between adjacent explosive grains which are representative of effective electromechanical response of CNT-polymer nanocomposites. The hierarchical framework developed here is used to explore key features of the NCBX microstructure, e.g. ratio of grain to nanocomposite stiffness, ratio of grain to nanocomposite conductivities etc., and related to the NCBX effective piezoresistive response. The results obtained from the current work show dependence of effective NCBX piezoresistive properties on each of these microstructural features with and without interfacial damage between the explosive grains.

The formation of hotspots within polymer bonded explosives can lead to the thermal decomposition and initiation of energetic materials. A frictional heating model is applied at the mesoscale in this study to assess the potential for the formation of hotspots under low velocity impact loadings. The frictional heating mechanism predominantly depends on the formation and growth of microstructural damage within the energetic material. Monitoring of the formation and growth of damage at the mesoscale is considered through the inclusion of piezoresistive carbon nanotube network within the energetic binder providing embedded strain and damage sensing. A coupled multiphysics thermo-electro-mechanical peridynamics framework is developed to perform computational simulations on an energetic material microstructure subject to low velocity impact loads. The coupled framework allows for the assessment of traveling compressive waves caused by impact with piezoresistive sensing, growth of damage with damage sensing and the possible formation of hotspots. The sensing mechanism has been shown to capture the presence of the compressive mechanical wave at different locations within the microstructure before large damage growth. It is observed that the development of hotspots is highly dependent on the impact energy. Higher impact energy leads to larger amounts of microstructural damage providing more damaged surfaces for friction to take place. The higher impact energy also yields larger relative velocities of sliding damage surfaces resulting in more frictional heating. With increase in impact energy, the model also predicts larger amounts of sensing and damage thereby supporting the use of carbon nanotubes to assess damage growth and subsequent formation of hotspots.

This paper builds on previous work done [1, 2] to explore the effective piezoresistive response of polymer bonded explosive (PBX) materials where the polymer medium is reinforced with carbon nanotubes (CNTs). In the present work, the nanocomposite binder is modeled explicitly as a piezoresistive material whose properties are determined from the nanoscale through a micromechanics based 2-scale hierarchical model connecting the nanoscale to the microscale grain structure. Electromechanical cohesive zones are used to model the interface between the grains and nanocomposite binder in order to characterize interface separation and the resulting piezoresistive effect. The overall microscale piezoresistive effect is measured by using the volume averaged properties of the microscale RVE. The hierarchical framework developed here is used to explore key features of the NCBX microstructure such as the effect of grain conductivity, weight percentage of CNTs used and nanocomposite gage factor.