Strain and Damage Sensing at the Mesoscale in Energetic Materials in Response to Localized Thermal Loads

摘要

Plastic bonded explosives (PBXs), consisting of high energy density energetic crystals in a polymer binder, area class of energetic materials which have been widely studied in regards to their shock and ignition response. Ofincreasing interest is the response of such energetic materials to non-shock mechanical insults, e.g. accidentaldrop and dynamic/vibration loads in transport, which have been observed to produce localized damage andthermal loading due to the formation of hot spots. In some cases, the formation of these hot spots can leadto sufficient levels of localized heating capable of sustaining chemical reactions and transitioning to detonation.While there are several proposed mechanisms which could drive the formation of hot spots, the primary driver(s)for sustaining the chemical reaction and triggering detonation are not well understood. This is in part due tothe diu000eculty in experimentally characterizing the distribution and interaction of hot spots at the mesoscale,given the small length and time scales over which they exist. Recently, Seidel and co-workers have explored theapplication of the distribution of carbon nanotubes within the binder phase of energetic materials as a means ofintroducing a signicant piezoresistive response within the energetic material. Doing this can provide a means forstrain and damage sensing at the mesoscale. While initial fabrication and testing of ammonium perchlorate andsugar-mock PDMS- and epoxy-binder energetic materials have provided initial proof-of-concept demonstrationsof strain and damage sensing, successful application towards locating and characterizing damage and hot spotsrequires greater understanding of the piezoresistive network at the mesoscale, and how it responds to localizedheating. In this work, a mesoscale model corresponding to a representative volume element of an energeticmaterial having a piezoresistive carbon nanotube nanocomposite binder is developed and subjected to localizedheating. An electro-thermo-mechanical peridynamics formulation is developed which includes the generation ofheat energy due to fracture and friction, and is applied to assess the diu000berences between strain and damagesensing. Eu000borts are also made to assess the response of the mesoscale sensing network to localized heating anddamage due to the presence of and interactions between increasing amounts of prescribed hot spots. Initialmodeling results from these simulations reveal that the distribution of localized heating (leading to interactionsbetween heat sources) and heating rate are strong indicators of whether or not such thermally induced damagewill propagate beyond its local origin.